perf: AvroRecordContext rebuilds a HoodieSchema wrapper and field map on every field access

[voonhous]

Describe the problem

AvroRecordContext#getFieldValueFromIndexedRecord is the implementation behind RecordContext#getValue for the Avro engine and runs once per record per accessed field in the file group reader flow: MOR snapshot reads, compaction, upsert log merging, and metadata table reads (ordering values, delete-flag checks, column value access).

Per invocation it:

• calls HoodieSchema.fromAvroSchema(record.getSchema()), allocating a fresh wrapper and re-deriving the schema type
• splits the field path with regex-based String.split
• calls HoodieSchema#getField on the fresh wrapper, which lazily rebuilds the entire field list and field map: one new HoodieSchemaField per column plus a HashMap collect, i.e. O(schema width) allocations per call
• wraps every union branch into another new HoodieSchema via getNonNullType

None of it is cached because the wrapper is thrown away after each call. For a 200-column table this is hundreds of allocations per record per accessed field.

The same per-record HoodieSchema.fromAvroSchema(...) rebuild also appears on other hot read / merge paths: Spark / Flink RecordContext#convertAvroRecord, the Hive MOR RealtimeCompactedRecordReader merge, HoodieAvroUtils#getRecordColumnValues, HoodieJsonPayload#getInsertValue, and the MERGE-INTO ExpressionPayload evaluators.

Proposed fix

Intern the Avro-schema -> HoodieSchema conversion so the canonical wrapper (and its lazily built field list / map) is reused across calls instead of allocating a fresh wrapper per record, keeping HoodieSchema as the facade (the lookup path is unchanged) rather than bypassing it with raw Avro traversal.

• Add an Avro-Schema-keyed cache (AvroToHoodieSchemaCache, identity / weakKeys) that converts and value-interns through HoodieSchemaCache on a miss, so equal-but-distinct Avro schema instances converge on one canonical HoodieSchema.
• Route the per-record call sites above through it; hoist the loop-invariant fromAvroSchema out of the per-record write loop in HoodieAvroDataBlock#getBytes. Leave cold / one-time and per-block sites unchanged.
• Make HoodieSchema#getFields / #getFieldMap publish their lazily built caches safely (volatile fields plus immutable wrappers), since interned instances are shared across executor task threads.

Results are identical for all valid inputs; the schema must keep coming from the record itself since log block schemas can differ from the reader schema.