fix: validate frame Dictionary_ID against the supplied dictionary

[jamesarich]

Closes an RFC 8878 conformance gap found in a parity audit: the decoder read a frame's Dictionary_ID field (§3.1.1.3) but never validated it.

Real libzstd sets a real Dictionary_ID by default when compressing with a proper Zstandard-format dictionary (zstd -D dictfile) and checks it on decode. kzstd previously decoded with whatever ZstdDictionary the caller passed regardless of what the frame declared, producing a generic corruption error deep in entropy decoding on a wrong-dictionary frame instead of a clear one.

What changed

• ParsedDictionary now captures a trained dictionary's own embedded Dictionary_ID (0 for raw-content dictionaries, matching the wire's "no ID" sentinel).
• The decoder compares the frame's declared ID against the supplied dictionary's ID when both are non-zero, throwing ZstdException with a message that names it as a dictionary-ID mismatch (not generic corruption).
• When either side is 0 — no field present, or a raw content dictionary — validation is skipped entirely. Fully backward compatible: kzstd's own encoder never sets a frame Dictionary_ID (confirmed spec-legal, unchanged by this PR), and raw content dictionaries keep working exactly as before.

Testing

• DictionaryIdValidationTest: pure parsing checks on every target (trained dict captures its embedded ID, raw-content/empty dicts read as ID 0, kzstd's own zero-ID frames still decode against a dictionary with a different ID).
• KzstdLibzstdInteropTest (zstd-jni oracle, real libzstd): compresses with real libzstd + the existing trained-dict fixture (already has a non-zero embedded ID), decodes with the correct dictionary (succeeds) and a different one (clear ZstdException).

No public API change — no apiDump needed.

./gradlew build passes on every target except native test-binary linking, which hits a pre-existing, unrelated crash on this dev host (reproduced on unmodified main, tracked in #56).

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📥 Commits

Reviewing files that changed from the base of the PR and between fba1059 and 960eb0e.

📒 Files selected for processing (6)

• CHANGELOG.md
• src/commonMain/kotlin/org/meshtastic/kzstd/internal/ParsedDictionary.kt
• src/commonMain/kotlin/org/meshtastic/kzstd/internal/ZstdDecoder.kt
• src/commonTest/kotlin/org/meshtastic/kzstd/DictionaryIdValidationTest.kt
• src/commonTest/kotlin/org/meshtastic/kzstd/TestVectors.kt
• src/jvmTest/kotlin/org/meshtastic/kzstd/KzstdLibzstdInteropTest.kt

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