fix(rxquery): emit yield/zero synchronously to keep element order - #25

Proposed Changes

Part of splitting #22 into small pull requests that can be reviewed one at a time. It is stacked on #24 (fix/map-async-max-concurrent), so it shows only its own change; merge #24 first.

Yield and Zero used Observable.Return/Empty (TimeProvider.System), which R3 schedules on the thread pool. Every element of a query therefore hopped to another thread, SelectMany merged them in arbitrary order and the results arrived after the source had moved on, so take, head, last, zip and friends were nondeterministic. Both now emit synchronously on subscription.

Types of changes

What types of changes does your code introduce to FSharp.Control.R3?
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• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

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• Build and tests pass locally – 0 warnings, Fantomas is clean, and the tests that exist at this commit pass
• I have added tests that prove my fix is effective or that my feature works (if appropriate) – in test: cover the library with integration tests #22, the top of this stack
• I have added necessary documentation (if appropriate)

Further comments

Tests (in #22): BuilderTests.fs – rxquery for and select project every element in order, rxquery over a synchronous source completes synchronously, rxquery if-then yield skips the other elements through Zero and every operator test that relies on the order.

Stack – every pull request is based on the one before it, so each shows only its own change. Merge them in this order:

1. refactor!: prefix AwaitOperationConfiguration cases with Await #23 refactor!: prefix AwaitOperationConfiguration cases with Await
2. fix: validate the concurrency limit of mapAsync options eagerly #24 fix: validate the concurrency limit of mapAsync options eagerly
3. fix(rxquery): emit yield/zero synchronously to keep element order #25 fix(rxquery): emit yield/zero synchronously to keep element order ← this pull request
4. fix(rxquery)!: stop seeding sumBy with Unchecked.defaultof #26 fix(rxquery)!: stop seeding sumBy with Unchecked.defaultof
5. feat(rxquery): add rxqueryWith to cancel the terminal query operators #27 feat(rxquery): add rxqueryWith to cancel the terminal query operators
6. docs(rxquery): document the query builder and every query operator #28 docs(rxquery): document the query builder and every query operator
7. feat(observable)!: make ofSeq reachable as Observable.ofSeq #29 feat(observable)!: make ofSeq reachable as Observable.ofSeq
8. feat(observable)!: make Observable.choose take a voption chooser, add ObservableOption #30 feat(observable)!: make Observable.choose take a voption chooser, add ObservableOption
9. feat(observable): add chunkByBoundaries for boundaries of any element type #31 feat(observable): add chunkByBoundaries for boundaries of any element type
10. fix(observable): validate every chunk length eagerly #32 fix(observable): validate every chunk length eagerly
11. docs: document the processing and chunk configuration types #33 docs: document the processing and chunk configuration types
12. docs(observable): correct misleading XML docs and document every function #34 docs(observable): correct misleading XML docs and document every function
13. fix(async)!: remove the ignored cancellationToken from toLookup #35 fix(async)!: remove the ignored cancellationToken from toLookup
14. fix(async)!: surface the original exception and cancellation from Async wrappers #36 fix(async)!: surface the original exception and cancellation from Async wrappers
15. fix: wait for iterAsync through ForEachAsync instead of CountAsync #37 fix: wait for iterAsync through ForEachAsync instead of CountAsync
16. fix: stop iterAsync reliably and never lose a failure of its action #38 fix: stop iterAsync reliably and never lose a failure of its action
17. fix(task)!: default ofTask configureAwait to true #39 fix(task)!: default ofTask configureAwait to true
18. feat(task)!: move toArray and toList into the Task.Observable module #40 feat(task)!: move toArray and toList into the Task.Observable module
19. docs: correct the Async and Task module docs and document every member #41 docs: correct the Async and Task module docs and document every member
20. docs: document the R3 1.3.1 limitations of bind, catch and mapAsync #42 docs: document the R3 1.3.1 limitations of bind, catch and mapAsync
21. test: categorize the tests per tested component #43 test: categorize the tests per tested component
22. test: cover the library with integration tests #22 test: cover the library with integration tests

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