Fix Apple queued write throughput (#271)

[fotiDim]

Fixes #271

• Pipeline consecutive writes on iOS, macOS, and Chrome on Apple platforms without crossing queued operation barriers.
• Add Darwin backpressure handling for writes without response and fail pending writes on disconnect.
• Complete Darwin write-with-response callbacks FIFO to support pipelined writes safely.

[Copilot]

Pull request overview

This PR improves write throughput on Apple platforms by allowing consecutive BLE writes to be pipelined (submitted before prior writes complete) while preserving queue-barrier semantics for non-write operations. It also adds Darwin-side handling for write-without-response backpressure and ensures write-with-response callbacks resolve FIFO to safely support pipelined writes.

Changes:

• Add a pipelining-capable queue path for writes (queueWrite + concurrent queue entries) while keeping non-write commands serialized behind write barriers.
• Enable supportsWritePipelining on iOS/macOS implementations (Pigeon + Web) and use it in UniversalBle.write.
• Update Darwin plugin to (a) backpressure writes without response, (b) fail pending writes on disconnect, and (c) resolve write-with-response futures FIFO; add tests + docs/changelog.

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
test/universal_ble_write_queue_test.dart	Adds regression tests for pipelined vs serialized writes and queue-barrier behavior.
test/universal_ble_test_mock.dart	Extends the platform mock to satisfy the updated platform interface (readRssi).
README.md	Documents Apple/Chromium-on-Apple pipelined write behavior and queue barriers.
lib/src/utils/ble_command_queue.dart	Adds queueWrite and routes pipelined writes through concurrent queue adds.
lib/src/universal_ble.dart	Uses queueWrite for write() and enables pipelining when the platform supports it.
lib/src/universal_ble_web/universal_ble_web.dart	Enables write pipelining on iOS/macOS targets for Web implementation.
lib/src/universal_ble_pigeon/universal_ble_pigeon_channel.dart	Enables write pipelining on iOS/macOS targets for native (Pigeon) implementation.
lib/src/queue.dart	Adds addConcurrent and concurrency gating to allow consecutive concurrent items.
lib/src/interfaces/universal_ble_platform_interface.dart	Introduces supportsWritePipelining capability flag (default false).
darwin/universal_ble/Sources/universal_ble/UniversalBlePlugin.swift	Implements backpressure for write-without-response, disconnect failure for pending writes, and FIFO completion for write-with-response.
darwin/universal_ble/Sources/universal_ble/UniversalBleHelper.swift	Adds PendingWriteWithoutResponse helper type.
CHANGELOG.md	Notes the Apple pipelined write throughput improvement.

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