[format] Support writing and reading Arrow schema metadata for file formats

[lxy-9602]

Purpose

This PR is a sub-PR for shared-shredding.

Shared-shredding needs to attach dictionary and other field-level metadata before closing data files. To support that flow, this PR adds a generic metadata write/read path for file formats, so upper layers can provide raw key-value metadata during writing, and readers can parse the stored metadata back when opening files.

The metadata representation follows Arrow Parquet's existing schema metadata convention: Arrow stores the original serialized schema under the ARROW:schema file metadata key, base64-decodes it on read, and deserializes it with Arrow IPC schema reading. See Apache Arrow's Parquet schema implementation, where kArrowSchemaKey is ARROW:schema and the value is base64-decoded before ReadSchema.

Related design:
https://cwiki.apache.org/confluence/display/PAIMON/PIP-43%3A+Columnar+Storage+Optimization+for+MAP+Type+in+Paimon

Brief change log

• Add SupportsWriterMetadata so format writers can accept raw Map<String, byte[]> metadata before file close.
• Add SupportsReaderArrowSchema so format readers can return the stored Arrow schema metadata.
• Add FormatMetadataUtils for:
  • base64 encoding metadata values before storing them in format footers;
  • base64 decoding stored metadata values;
  • reading the fixed ARROW:schema key into an Arrow Schema;
  • extracting field-level metadata as Map<String, Map<String, String>>.
• Support metadata writing for Parquet and ORC writers.
• Support Arrow schema metadata reading from Parquet and ORC readers.
• Add Parquet/ORC tests covering metadata write/read and field-level Arrow metadata roundtrip.

Compatibility

The metadata value is stored using Arrow-compatible base64 encoding. For Arrow schema metadata, the key is ARROW:schema, matching Arrow Parquet's convention.

Tests

mvn -pl paimon-format -am -Pfast-build -DfailIfNoTests=false \
  -Dtest=ParquetFormatReadWriteTest#testWriteMetadata,OrcFormatReadWriteTest#testWriteMetadata,FormatMetadataUtilsTest test