Restore emitter timing instrumentation (console.time) in $onEmit for testing

[Copilot]

This PR restores the console.time / console.timeEnd instrumentation that was removed in #3483. The goal is to bring back timing visibility in the TypeSpec emitter pipeline for testing and performance observation.

• What changed

  • Reintroduced timing markers in packages/typespec-ts/src/index.ts inside $onEmit.
  • Restored the original phase-level labels across key emitter stages (context creation, static helper loading, binder setup, RLC model build, modular source generation sub-phases, and overall emit duration).

• Lint-scope handling

  • Kept no-console enforcement intact by applying // eslint-disable-next-line no-console only on restored timing lines, instead of broad file/function-level suppression.

• Illustrative snippet

  // eslint-disable-next-line no-console
  console.time("onEmit: create context");
  const dpgContext = await createContextWithDefaultOptions(context);
  // eslint-disable-next-line no-console
  console.timeEnd("onEmit: create context");

Original prompt

#3483
这个pr吧console.time 给删除了，现在需要一个用来做testing的pr，需要把console.time 加回原来的位置

[Chronological Review: The conversation began with the user requesting modifications to the function `knownMediaType` to handle a specific case for the "/" character. The user then inquired about potential modifications in another file, `transformParameters.ts`, and asked various questions regarding the code logic, particularly around the handling of different content types and encoding. The user also requested to add back `console.time` in a specific pull request for testing purposes.]

[Intent Mapping:

1. "当前代码里的'/的逻辑做进function knownMediaType里面，增加if条件，/时return KnownMediaType.Binary，并修改对应代码" - User wants to modify the knownMediaType function.
2. "packages/typespec-ts/src/transform/transformParameters.ts 是不是也要修改？" - User is checking if another file needs modification.
3. "为什么111行是uint8ArrayToString" - User is questioning a specific line of code.
4. "tcgc 处理的逻辑在哪里" - User is looking for the logic related to tcgc.
5. "什么情况会是Scalar" - User is asking about conditions for a scalar type.
6. "SchemaContentTypeValues 是一个union，是不是算!defaultContentType" - User is inquiring about union types.
7. "抛开*/的问题，重新分析为什么111行是uint8ArrayToString" - User wants a deeper analysis of a specific line.
8. "为什么type.kind === 'Scalar' 且无 defaultContentType" - User is questioning a specific condition in the code.
9. "路径一里面为什么会是这个结果" - User is asking about a specific result in the code.
10. "那为什么有些 bytes 不会又encode base64？" - User is inquiring about encoding behavior.
11. "那什么时候tcgc没有encode？" - User is asking about conditions when tcgc does not encode.
12. "都会有encode那岂不是不会走到else {...}" - User is questioning the logic flow.
13. "当前case加一个content-type是application/xml的" - User wants to add a specific content type case.
14. "SCENARIOS_UPDATE设置为true并且跑一下这个的ut packages\typespec-ts\test\modularUnit\scenarios\operations\bodyParam\bytesWithDifferentContentType.md" - User is requesting to run a unit test with a specific setting.
15. "Continue: 'Continue to iterate?'" - User is prompting to continue the iteration.
16. "这个pr吧console.time给删除了，现在需要一个用来做testing的pr，需要把console.time加回原来的位置" - User is requesting to add back console.time in a specific pull request for testing.]

[Technical Inventory:

• Function knownMediaType: Needs modification to handle "/" character.
• File transformParameters.ts: Potential modifications discussed.
• Content types: Various types discussed including application/xml.
• Encoding logic: Questions raised about when encoding occurs and the behavior of tcgc.]

[Code Archaeology:

• knownMediaType: Function to be modified.
• transformParameters.ts: File under consideration for changes.
• Specific lines of code questioned: Line 111 regarding uint8ArrayToString, and conditions for scalar types.]

[Progress Assessment:

• Completed: User has made several inquiries and requests for modifications.
• Pending: Modifications to knownMediaType, potential changes in transformParameters.ts, and adding back console.time in the PR.]

[Context Validation: All user requests and inquiries are captured, providing a clear path for continuation.]

[Recent Commands Analysis:

• Last Agent Commands: User requested to modify the knownMediaType function and check another file for necessary changes.
• Tool Results Summary: No specific tool results were returned as the conversation primarily consisted of user inquiries and requests.
• Pre-Summary State: The agent was actively discussing modifications to the code and addressing user inquiries when the token budget was exceeded.
• Operation Context: The user is focused on refining the codebase and ensuring proper handling of media types and encoding.]

1. Conversation Overview: - Primary Objectives: User requested modifications to the `knownMediaType` function to handle the "/" character and inquired about related logic in other files. User also asked various questions about encoding, content types, and specific lines of code. - Session Context: The conversation has revolved around understanding and modifying code logic, particularly in the context of media types and encoding. - User Intent Evolution: The user has shifted from specific function modifications to broader inquiries about code behavior and testing requirements.

2. Technical Foundation:

• Function knownMediaType: Needs to be modified to return KnownMediaType.Binary for the "/" character.
• File transformParameters.ts: Potential modifications discussed.
• Content Types: User wants to add handling for application/xml.
• Encoding Logic: User is exploring when encoding occurs and the behavior of tcgc.

3. Codebase Status:

• File Name: index.ts
• Purpose: Core functionality related to media type handling.
• Current State: User is requesting modifications and clarifications on specific lines.
• Key Code Segments: Line 111 regarding `uint8ArrayToString...

Created from VS Code.

[kazrael2119]

#3907