Adds parallel branch execution to the .NET Durable Execution SDK.
ParallelAsync runs N branches concurrently with configurable concurrency
limits and completion policies, returning an IBatchResult<T> with
per-branch status and error information.

Per-branch checkpoint payloads are serialized via the ILambdaSerializer
registered on ILambdaContext.Serializer (typically configured through
LambdaBootstrapBuilder.Create(handler, serializer)), matching the
StepAsync / RunInChildContextAsync pattern. There are no separate
reflection / AOT-safe overload pairs: the AOT story is determined
entirely by which serializer the user registers with the runtime.

Public surface:
- IDurableContext.ParallelAsync<T> (2 overloads: Func[] vs
  DurableBranch<T>[])
- DurableBranch<T> record (Name + Func)
- ParallelConfig (MaxConcurrency, CompletionConfig, NestingType)
- CompletionConfig with factories AllSuccessful() / FirstSuccessful() /
  AllCompleted(); ToleratedFailureCount / ToleratedFailurePercentage
  (validated 0.0-1.0)
- IBatchResult<T> with All / Succeeded / Failed / Started accessors,
  GetResults, GetErrors, ThrowIfError, HasFailure, CompletionReason,
  count properties
- IBatchItem<T> with Index, Name, Status, Result, Error
- BatchItemStatus { Succeeded, Failed, Started }
- CompletionReason { AllCompleted, MinSuccessfulReached,
  FailureToleranceExceeded }
- NestingType (Nested default; Flat throws NotSupportedException - reserved)
- ParallelException (carries IBatchResult; future-subclassable)

Internal:
- ParallelOperation<T> orchestrator dispatches branches with optional
  semaphore-bounded concurrency. Each branch runs as a
  ChildContextOperation<T> with deterministic ID via
  OperationIdGenerator.CreateChild.
- Branch failures aggregated as IBatchItem<T> entries; orchestrator
  throws ParallelException only when CompletionConfig signals
  FailureToleranceExceeded.
- Parent CONTEXT checkpoint records summary (CompletionReason +
  per-branch index/name/status); branch results live on per-branch
  CONTEXT checkpoints.
- ExecutionState now thread-safe (lock around reads/writes of
  _operations, _visitedOperations, _isReplaying). Required for
  concurrent branch replay; affects all operations but no regressions.
- ParallelOperation awaits Task.WhenAll(inFlight) before disposing
  the semaphore so cancellation/exception during dispatch lets
  in-flight branches settle cleanly.
- Reuses OperationSubTypes.Parallel / OperationSubTypes.ParallelBranch
  from Wave 0.

Adds 31 unit tests + 6 integration tests covering CompletionConfig
matrix, MaxConcurrency, FirstSuccessful short-circuit, replay
determinism, mixed-status replay, cancellation, and concurrency
stress.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

fix tests

change file

Validate CompletionConfig thresholds and honor checkpointed branch names

- Add range validation to CompletionConfig.MinSuccessful (>= 1) and
  ToleratedFailureCount (>= 0), matching the existing
  ToleratedFailurePercentage setter. Previously zero/negative values
  produced nonsensical immediate short-circuits.
- ReconstructFromCheckpoints now uses the branch Name persisted in the
  parallel summary instead of always reading the current branch name,
  and throws NonDeterministicExecutionException on name drift between
  deployments (the prior path silently ignored summaryEntry.Name).
- Correct XML docs for BatchItemStatus.Started / IBatchResult.Started /
  CompletionConfig.FirstSuccessful: Started means a branch was not
  dispatched before a completion short-circuit fired (or has no
  checkpoint on replay), not that it is still running.

Implements IDurableContext.MapAsync, processing a collection in parallel
with one child context per item. Mirrors the Python/JS/Java SDKs, where
Map is a sibling of Parallel sharing one concurrency engine.

- Extract ConcurrentOperation<T> base holding all orchestration, completion,
  checkpoint, and replay logic; ParallelOperation and MapOperation are thin
  subclasses supplying only the per-unit (name, func), sub-type labels, and
  failure-exception factory.
- MapConfig defaults CompletionConfig to AllCompleted() (permissive), matching
  Python/Java Map; intentionally differs from ParallelConfig's AllSuccessful().
  Adds ItemNamer; no ItemBatcher (not implemented in any reference SDK).
- New MapException so callers can distinguish Map from Parallel failures.
- Generalize ParallelSummary/ParallelJsonContext into shared BatchSummary/
  BatchJsonContext.
- Tests: 24 unit tests (MapOperationTests) + 6 integration functions/tests
  mirroring the Parallel set. Full suite 325/325 on net8.0 and net10.0.