Release mp4forge 0.8.0 with mux support, streaming fixes, and broader media coverage

[bakgio]

Summary

This prepares mp4forge 0.8.0 and lands the branch work since 0.7.0. The release adds the feature-gated mux surface, expands media import and fragmented output coverage, improves streaming/file-backed behavior, broadens validation and regression coverage, and updates release-facing docs.

Added

• Added the mux feature with MuxRequest, path-first MuxTrackSpec parsing, flat and fragmented output layouts, segment/fragment duration modes, sync APIs, async APIs behind mux + async, and the sync-only mux CLI.
• Added real MP4 mux writing for flat and fragmented layouts, including split init/media fragmented output helpers.
• Added destination update-or-create mux behavior for flat output, including preservation of existing destination tracks and selected destination metadata where supported.
• Added broad path-first import coverage for MP4 tracks, selected container formats, elementary audio/video inputs, image inputs, raw-video inputs, PCM inputs, subtitle/text inputs, local manifest inputs, and sidecar-style mux reports.
• Added mux inspection, sample-reader, and elementary sample rewrite/export helpers.
• Added new mux examples and expanded retained fixtures.
• Added new fuzz targets for mux demuxing, mux sample rewrites, async API parity, decrypt byte-surface parity, additional box roundtrips, bit I/O boundaries, and sidx plan application.

Changed

• Updated package metadata, README install snippets, issue template version placeholder, and changelog for 0.8.0.
• Broadened typed box/sample-entry coverage used by mux, probe, divide, decrypt, and rewrite flows.
• Improved divide/probe support for additional video and audio sample-entry families.
• Reworked supported decrypt rewrite paths to use streaming root rewrite plans and refreshed affected top-level sidx data after clear-output rewrites.
• Moved tests and helpers toward auto-cleaned temporary paths and tightened regression coverage around sync/async parity.

Removed

• Removed deprecated dump command shorthand options -mdat and -free; callers should use -full mdat or -full free,skip.