[Repo Assist] Add AsyncSeq.mapAsyncParallelThrottled — ordered, bounded-concurrency parallel map

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Summary

Adds AsyncSeq.mapAsyncParallelThrottled, completing the parallel map API matrix:

Function	Order preserved	Concurrency
mapAsyncParallel	✅ ordered	unbounded (ThreadPool)
mapAsyncUnorderedParallel	❌ unordered	unbounded (ThreadPool)
mapAsyncUnorderedParallelThrottled	❌ unordered	bounded (parallelism)
mapAsyncParallelThrottled	✅ ordered	bounded (parallelism) ← NEW

Motivation

Users often want ordered results (predictable output order, easy diffing, deterministic logging) but also want to cap resource usage — e.g. limiting HTTP connections, database queries, or expensive computations to N concurrent operations. Previously this required building a custom wrapper around mapAsyncParallel or using the unordered variant and accepting non-deterministic output order. mapAsyncParallelThrottled fills this gap directly.

API

/// Builds a new asynchronous sequence whose elements are generated by
/// applying the specified function to all elements of the input sequence,
/// with at most <c>parallelism</c> mapping operations running concurrently.
///
/// The function is applied to elements in order and results are emitted in order,
/// but in parallel, with at most <c>parallelism</c> operations running concurrently.
/// This is the throttled counterpart to <c>mapAsyncParallel</c>.
val mapAsyncParallelThrottled : parallelism:int -> mapping:('T -> Async<'U>) -> s:AsyncSeq<'T> -> AsyncSeq<'U>

Implementation

The implementation combines the ordering logic of mapAsyncParallel (child tasks posted in order, awaited in order) with the SemaphoreSlim throttling from mapAsyncUnorderedParallelThrottled. The semaphore is acquired before starting each task and released when the task completes (success or exception), naturally bounding in-flight work.

Changes

• src/FSharp.Control.AsyncSeq/AsyncSeq.fs — implementation
• src/FSharp.Control.AsyncSeq/AsyncSeq.fsi — signature with XML-doc
• tests/FSharp.Control.AsyncSeq.Tests/AsyncSeqTests.fs — 3 new tests (order preservation, exception propagation, throttle enforcement)
• RELEASE_NOTES.md — 4.14.0 entry
• version.props — bumped to 4.14.0

Test Status

✅ Build: succeeded (0 errors, pre-existing warnings only — NU1605, FS9999)
✅ .NET tests: 414/414 passed (3 new tests for mapAsyncParallelThrottled)

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Commit pushed: 41e69f1

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🤖 Repo Assist here.

Root cause of Fable CI failure: System.Threading.Channels Version="*" resolved to 10.0.6, which requires Microsoft.Bcl.AsyncInterfaces >= 10.0.6. But the project pinned it at 10.0.5, producing a NU1605 downgrade warning. Fable's MSBuildCrackerResolver treats NU1605 as a fatal error, crashing before compilation begins.

Fix applied: Bumped Microsoft.Bcl.AsyncInterfaces from 10.0.5 → 10.0.6 in FSharp.Control.AsyncSeq.fsproj. All 414 .NET tests still pass.

Note: this is a pre-existing issue unrelated to the mapAsyncParallelThrottled feature — it would have affected the main branch too once System.Threading.Channels 10.0.6 was released.

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