feat: pause and resume FFmpeg sessions

[sheehanmunim]

Closes #11.

What

• pause(sessionId): boolean: pauses an execute() session, whether running or queued.
• resume(sessionId): boolean: resumes a paused session.
• getSessionState(sessionId): returns queued, running, paused, completed, failed, cancelled or unknown.

How

This does a real pause, rather than the cancel-and-restart-with--ss approach suggested in the issue, which re-encodes around the seek point and can drift. FFmpeg 9's fftools runs demuxing, decoding, filtering, encoding and muxing on separate threads. The patch in scripts/ffmpeg/fftools-hooks.sh makes the threads that bring data into the pipeline wait while their session is paused:

• Demuxer threads wait before each av_read_frame, and shift their -re/-readrate wallclocks by the time spent paused so they don't burst afterwards.
• Filtergraphs with no inputs (-filter_complex testsrc and similar) wait before pulling frames.

Everything downstream drains and idles, so a paused session uses no CPU. Output stays open, and resuming continues from the exact packet where reading stopped. The execute() promise settles once. cancel()/cancelAll() wake a paused session and cancel it as before, and a queued session can be paused so that it starts paused.

The core keys pauses on the numeric session ID through the new munim_ffmpeg_execute_session / munim_ffmpeg_probe_session entry points; the old entry points use ID 0. The Android bridge creates a new JNI global reference for every run, so the callback pointer can't identify a session. FFprobe sessions report their state but can't be paused.

Verified so far

• A native harness links the real munim_ffmpeg_core.c against a fake ffmpeg_main reader thread. It checks:
  • no progress while paused;
  • the run completes after resume, and the hook reports the time spent paused;
  • cancel while paused returns 255;
  • a queued session starts paused and completes after resume;
  • unknown and zero IDs do nothing.
• The fftools patch applies cleanly to FFmpeg 9.0.2, and fails on anchor drift.
• tsc (package and example) and eslint pass.

Still to do: run the device suite (two new checks) on the Galaxy A14 and the iPad Air M3 against binaries built by this PR's build-binaries run.

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[sheehanmunim]

🎉 This PR is included in version 0.8.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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