fix: reject malformed metadata file versions - #846

Summary

• reject malformed and out-of-range version segments in metadata filenames instead of accepting a valid numeric prefix
• start generated metadata filenames at version 0 when the current version cannot be parsed, matching Java
• add coverage for trailing characters, overflow, and an empty version segment through the metadata write path

Testing

• arrow_test --gtest_filter=MetadataIOTest.WriteMetadataWithBase
• full CTest suite (17 test binaries)