chore: bump avro to 209a373 to preserve adjust-to-utc on primitives

[manuzhang]

What

Moves the avro-cpp pin in cmake_modules/IcebergThirdpartyToolchain.cmake from 997d50d to 209a373 (current apache/avro main, 74 commits ahead). The C++ changes in the range:

• AVRO-4351 (209a373): avro-cpp now keeps custom attributes on primitive schema nodes when parsing and printing schema JSON.
• 6444e8d: std::formatter for avro::Name/avro::Type templated on the format context, fixing C++23 builds.
• cc134b3: JSON decoder rejects the lone low surrogate U+DFFF.

Adds tests that pin AVRO-4351:

• AvroSchemaProjectionTest.ProjectTimestampTzFromParsedAdjustToUtc / RejectTimestampFromParsedAdjustToUtc — parse adjust-to-utc from schema JSON and project timestamptz, timestamptz_ns and timestamp against it.
• AvroReaderParameterizedTest.TimestampTzTypes — write timestamptz and timestamptz_ns columns to a file and read them back, in both decoder modes.
• AvroWriterTest.WriteTimestampTzTypes — write all four timestamp types, assert adjust-to-utc is present on each primitive node in the physical file schema, and read the data back, in both encoder modes.

Adds a comment on GetAdjustToUtc() recording why the pin matters.

Why

GetAdjustToUtc() reads adjust-to-utc off the primitive Avro node, and ValidateAvroSchemaEvolution gates timestamp vs timestamptz on it. The reader takes its file schema from the Avro file header, which avro-cpp parses from JSON. Before AVRO-4351, Compiler.cc only collected custom attributes for records, arrays and maps, and NodePrimitive::printJson never emitted them. So the attribute was lost twice: the writer dropped it from the file header, and the reader dropped it when parsing. Every timestamp read from a file then looked like it had no timezone, and projecting a timestamptz or timestamptz_ns column out of an Avro file failed with Cannot read Iceberg type: timestamptz from Avro type: ....

No test wrote and re-read a timestamptz column through a real file — the existing round trips use TimestampType only, and the timestamptz cases in avro_data_test.cc build the node in memory with ToAvroNodeVisitor — which is why this went unnoticed.

Behavior change

• timestamptz and timestamptz_ns columns can now be read from Avro files.
• Avro files written by iceberg-cpp now carry adjust-to-utc on timestamp primitives in the file header schema, as the Iceberg spec requires.

Testing

Built locally with gcc 15 at C++23 against the new pin and ran avro_test: 244/244 pass, including the 6 new tests (parameterized variants included). Rebuilt against the old pin 997d50d: the same 6 tests fail — reader/projection tests with Cannot read Iceberg type: timestamptz ..., writer test with node->customAttributes() being 0 — confirming they pin the fix. clang-format --dry-run -Werror and git diff --check are clean on the changed files.

🤖 Generated with Claude Code

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[wgtmac]

Thanks for the quick update!