Update C++ module bindings to RawModuleDefV10

[JasonAtClockwork]

Description of Changes

• Migrated the C++ module-definition assembly path to V10-first internals:
  • Added v10_builder and module_type_registration systems.
  • Switched Module::describe_module to serialize RawModuleDef with V10 payload.
  • Updated macro registration pipeline to register through V10
• Added explicit naming support across macro surface (*_NAMED variants for reducer/procedure/
  view and field/index macros).
• Reworked multi-column index macros (FIELD_MultiColumnIndex, FIELD_MultiColumnIndex_NAMED) with
  migration alias.
• Added SPACETIMEDB_SETTING_CASE_CONVERSION(...) to support case conversion policy
• Error-path hardening by adding explicit constraint-registration error tracking and preinit validation
• Codegen updates:
  • Updated C++ moduledef regen to V10 builder types.
  • Adjusted C++ codegen duplicate-variant wrapper generation to emit proper product-type
    wrappers.
• Test/harness updates:
  • type-isolation-test runner now defaults to focused V10 regression checks; --v9 runs broader
    legacy/full suite.
  • Added focused modules for positive/negative V10 checks:
    • test_multicolumn_index_valid
    • error_multicolumn_missing_field
    • error_default_missing_field
• Re-enabled C++ paths in sdks/rust/tests/test.rs procedure/view/test suites.

API and ABI breaking changes

• Refactor of the underlying module definition
• New *_NAMED variant macros for explicit canonical naming
• FIELD_NamedMultiColumnIndex renamed to FIELD_MultiColumnIndex

Expected complexity level and risk

3 - Large set of changes moving over to V10 with underlying changes to make future updates a little easier

Testing

• Ran the type isolation test and expanded it
• Ran the spacetimedb-sdk test framework to confirm no more drift between C++ and other module languages
• Ran Unreal test suite though not really applicable
• New app creation with spacetime init --template basic-cpp
• Ran describe module tests against Rust + C# matching with C++ on the /modules/sdk-test* modules to find any possible mis-alignment

Review

• Another look at the new features with C++
• Thoughts on *_NAMED macros, I couldn't come up with a better solution with C++20

[rekhoff]

This looks good overall, with a few minor items. In response to the specific Reviewer questions:

• This looks to cover the V10 code paths and lines up with the work I had done in C#.
• As for the *_NAMED macros, I can't think of a better solution with C++20.

[rekhoff]

Changes look good. All reviewer items addressed, marking my approval.