feat: Honor write.metadata.path for metadata file locations

[zakariya-s]

Which issue does this PR close?

• Closes Honor write.metadata.path table property for metadata file locations #2775.

What changes are included in this PR?

Metadata files were always written under <table-location>/metadata, ignoring the write.metadata.path table property. Iceberg Java honors it (via BaseMetastoreTableOperations.metadataFileLocation); this brings iceberg-rust in line and mirrors the existing write.data.path handling for data files.

• Add TableMetadata::metadata_location_root(), returning write.metadata.path (trailing slash trimmed) when set, otherwise <location>/metadata.
• Use it in SnapshotProducer for the manifest and manifest-list paths, and in MetadataLocation for the table metadata JSON.
• MetadataLocation now stores the resolved metadata directory rather than the table location. On commit, the directory is re-derived from the metadata being committed (the version is still parsed from the previous file name), matching Iceberg Java. As a result MetadataLocation::from_str no longer requires the file to live under a /metadata directory (a custom write.metadata.path does not have to); file-name validation is unchanged.

Are these changes tested?

Unit tests:

• TableMetadata::metadata_location_root(): default, configured write.metadata.path, and trailing-slash trimming.
• MetadataLocation: create (new_with_metadata) and commit (with_new_metadata) honor write.metadata.path; from_str round-trip cases updated for arbitrary metadata dirs.
• A fast_append transaction test asserting the manifest list and manifests are written under a configured write.metadata.path.
• Updated catalog::tests::test_table_commit to reflect the new metadata file following the updated table location.

[zakariya-s]

Thank you for the review @andybradshaw! I think I've addressed them so far, please do let me know if there are any other flags you can see

[andybradshaw]

Seems fine to me, but will need to get another review/approval from a maintainer.

[xanderbailey]

Thanks for the PR, just one comment I think

[zakariya-s]

Thanks @xanderbailey! I think I've addressed the comment. I did notice though that write.data.path isn't fetched from TableProperties:

iceberg-rust/crates/iceberg/src/writer/file_writer/location_generator.rs

Lines 60 to 62 in b80ebbf

	let configured_data_location = prop
	.get(WRITE_DATA_LOCATION)
	.or(prop.get(WRITE_FOLDER_STORAGE_LOCATION));

Might create an issue for this later if you think it's worth it