feat(parquet): support parquet metadata cache

[gripleaf]

Purpose

Support caching raw Parquet metadata footer bytes to reduce repeated footer reads and metadata deserialization when opening the same Parquet files in one process.

This change:

• Adds CacheKind::PARQUET_METADATA.
• Adds CacheKey::ForParquetMeta(file_uri) for footer cache keys.
• Injects cache into reader builders through WithCache.
• Caches raw Parquet footer bytes in ParquetReaderBuilder.
• Passes cached parquet::FileMetaData into ParquetFileBatchReader::Create.
• Reuses a shared counting cache test utility for manifest and Parquet metadata cache tests.

Tests

• ParquetFileBatchReaderTest.TestParquetMetadataRawBytesCacheReusesFooter
• ParquetFileBatchReaderTest.TestParquetMetadataCacheBypassesWhenGetUriFails
• WriteAndReadInteTest.TestAppendWithParquetMetadataCache

API and Format

This change affects public API in include:

• Adds CacheKind::PARQUET_METADATA.
• Adds CacheKey::ForParquetMeta.
• Adds ReaderBuilder::WithCache.

This change also updates the internal Parquet reader creation path to accept an optional parquet::FileMetaData.

No storage format or protocol change.

Documentation

Yes. Added docs/source/user_guide/parquet_metadata_cache.rst and linked it from the user guide.

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Generated-by: OpenAI Codex (GPT-5)