Sequence Guard, ordered execution, ConditionTransfer cleanup

Sequence Guard for AsyncConvertTransfer and AsyncConditionTransfer

• Bug fix (issue #7): Race condition on _state.value when maxConcurrency > 1. Parallel async operations shared a single ProxyReference<T>, so a faster operation could overwrite or clear _state.value before a slower one emitted — subscribers received stale or undefined values, and emissions arrived out of order.
• Sequence Guard: When maxConcurrency > 1, each operation receives a monotonic sequence number. Results are placed into an internal PendingResultQueue and emitted to subscribers strictly in data-arrival order. A faster result waits in the queue until all preceding operations have emitted. When maxConcurrency <= 1, the guard is inactive (zero overhead, backward-compatible).
• AsyncConditionTransfer.shouldEmit now receives the operation's local data: T instead of the shared _state.value, eliminating cross-operation data leakage. The _state is written only at emission time inside the guarded _drain().
• AsyncConditionTransfer.shouldEmit signature narrowed from (currentState: T | undefined) => Promise<boolean> | boolean to (data: T) => Promise<boolean> | boolean — undefined is no longer possible at runtime. Backward-compatible via contravariance (a function accepting T | undefined is assignable to a parameter expecting T).
• AsyncConvertTransfer and AsyncConditionTransfer destroy() now clears the pending result queue.
• New helper classes (src/helpers.ts): PendingResultQueue<T> (ordered result queue with nextSeq()/submit()/drain()/clear()) and OrderedExecutor (sequential async task executor with submit()/reset()).

Ordered execution for AsyncSinkTransfer and AsyncWriteTransfer

• New config option ordered?: boolean added to AsyncSinkTransferConfig and AsyncWriteTransferConfig (default: false, backward-compatible). When enabled, callback / flow.write() invocations are executed sequentially in data-arrival order via an internal OrderedExecutor (promise chain). The chain catches errors per-task so a throwing task does not block subsequent tasks; the error is still propagated to the asyncPush caller.
• destroy() on both transfers now resets the executor.

ConditionTransfer cleanup

• trigger() method removed from ConditionTransfer. It was not part of any implemented interface (isTriggerable was never set to true), and its existence created a race condition: shouldEmit could receive undefined from _state.value after _state.clear() in a prior push(). The push() method now inlines the shouldEmit check directly with the incoming data: T, making undefined impossible.
• ConditionTransferConfig.shouldEmit signature narrowed from (currentState: T | undefined) => boolean to (data: T) => boolean — undefined is no longer possible at runtime. Backward-compatible via contravariance.
• README: Removed !== undefined guards from shouldEmit examples for both ConditionTransfer and AsyncConditionTransfer.

Infrastructure

• API docs generator: typedoc added as devDependency; npm run docs script generates API reference to docs/api.
• GitHub Actions: deploy-docs.yml workflow added — generates and deploys API docs to GitHub Pages on push to master.
• .gitignore: docs directory added.
• interfaces.ts: Unused OutputTransfer import removed.

Tests

• Sequence Guard tests: Added race-condition regression tests for AsyncConvertTransfer (287 tests) and AsyncConditionTransfer (459 tests) — covering parallel ordered emission, stale-result prevention, failed-operation queue advancement, and destroy() queue cleanup.
• Ordered execution tests: Added tests for AsyncSinkTransfer (264 tests) and AsyncWriteTransfer (284 tests) covering ordered callback/write execution, error isolation, and destroy() reset.
• Helper tests: Added PendingResultQueue (237 tests) and OrderedExecutor (355 tests) test suites.
• ConditionTransfer tests: Removed 3 tests that used trigger() manually; renamed 2 tests from "trigger" to "shouldEmit" naming; removed !== undefined guards from shouldEmit predicates.
• Coverage: Maintained 100% test coverage (statements, branches, functions, lines) across all 11 source files. Total tests: 2,086.