feat(ebml-iterable): add incremental decoder

[irvingouj@Devolutions (irvingoujAtDevolution)]

Adds a vendored fork of ebml-iterable 0.6.3 for parsing append-only EBML streams.

The new TagDecoder keeps incomplete headers and payloads pending until more bytes arrive. Callers report real end-of-input through decode_eof, so growing recording files no longer need seek, rollback, sleep, or temporary-EOF retry logic.

The fork preserves Austin Blake's MIT license and records the upstream commit in its README. The existing iterator and the incremental decoder share header and data-tag parsing.

Validation:

• cargo check -p ebml-iterable --lib
• cargo clippy -p ebml-iterable --lib -- -D warnings
• Tests were not run in this session.

Issue: N/A

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