test: cover the library with integration tests - #22

`ProcessingOptionsTests` pin `Default`, `Parallel`, and the
`AwaitOperation` and `MaxConcurrent` of every
`AwaitOperationConfiguration` case.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

`ChunkTests` cover `chunkBySize`, `chunkBy` for every
`ChunkConfiguration` case with time driven by `FakeTimeProvider`,
`chunkByBoundaries` and the `ChunkConfiguration` helpers: empty
sources, resumed errors, failures, eager validation, window tokens,
disposal and `ConfigureAwait`.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Replaces the `Thread.Sleep` test with deterministic tests of the rxquery
builder over R3 1.3.1: `for`, `yield`, `zero` and every custom operation
in order and with synchronous completion, empty sources, terminal
failures and `OnErrorResume`, short-circuit disposal on hot subjects,
the `sumBy` regressions and the `rxqueryWith` token.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Replaces the two smoke tests with tests of every function of the
Observable module except chunking and rxquery, against R3 1.3.1 with
synchronous sources: values, errors reported through `OnErrorResume`
and completion for each wrapper, terminal failures, empty sources,
disposal and unsubscription proven on open subjects, `choose` and
`ObservableOption.choose`, and `ofSeq`, including its R3 behaviour with
cancellation, enumeration exceptions and early unsubscription.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Exercise both flavours of mapAsync (Task and Async, one data row each)
against R3 1.3.1 SelectAwait: every await operation, CancelOnCompleted,
source failures, selector exceptions, resumed source errors, empty
sources, the eager concurrency-limit validation, disposal and the
ConfigureAwait option. Gated selectors and awaited signals keep every
test deterministic; the unlimited parallel cases complete the source
before releasing the last selector to avoid the R3 completion race.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Exercise every function of `FSharp.Control.R3.Async` against R3 1.3.1:
the cold subscription of `length`, `aggregate`, `all`, `existsAsync`,
`firstAsync`, `iter`, `toArray`, `toList`, `ofAsync`, `iterAsync`, a
default `mapAsync` projection and the four `toLookup` overloads,
including the positional `keyComparer` and `elementSelector` calls that
the removed `cancellationToken` parameter used to swallow.

Every terminal function is checked for raising the original exception
of a source failure or `OnErrorResume`, for cancellation through the
Async token, for keeping no subscription with a cancelled token and for
resuming on the synchronization context it started to wait on.
`iterAsync` is checked for every way it used to keep running, hang or
lose a failure of its action.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Cover every function of `FSharp.Control.R3.Task` except the selector
modes of `mapAsync`, against R3 1.3.1 behaviour and deterministically:

- `length`, `aggregate`, `all`, `existsAsync`, `firstAsync`, `iter`,
  `toArray` and `toList` for values, empty sources, short-circuiting
  and callback exceptions.
- `iterAsync`: order, failures of the action, including a late one and
  an `OperationCanceledException` of its own, synchronous sources,
  cancellation of the running action, and eager rejection of an invalid
  concurrency limit.
- `ofTask` (both overloads): synchronous emission, one invocation per
  subscription, failures, disposal, and `configureAwait` defaulting to
  `true`, observed through a recording synchronization context.
- Every `toLookup` overload, positional, with and without a token,
  including the empty lookup.
- Every terminal function, through data rows: terminal failures and
  resumed errors fault with the same exception, and cancellation
  disposes the subscription, both while waiting and up front.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

- A hot subject through filter, distinct, mapi and chunkBySize, including
  a failed completion, a resumed predicate error and disposal.
- Merged sources behind catch: the fallback, an unhandled exception type
  and resumed errors, each unsubscribing from the source still open.
- The Task and Async terminal functions agree on the same pipeline, on an
  empty one, and fail with the same exception instance.
- mapAsync failures and cancellation of the terminal function, time
  chunks driven by FakeTimeProvider, ofTask and ofAsync inside bind,
  rxquery feeding both flavours, chunkByBoundaries with a unit trigger
  feeding choose, and ofSeq feeding a whole pipeline.

The type abbreviations are wrapped in a file-specific module, because
namespace-level abbreviations with the same names in another test file
fail to compile with FS0249.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>