AVRO-4253: [java] Bound FastReaderBuilder record-reader cache to fix memory leak

[iemejia]

What changes were proposed in this pull request?

FastReaderBuilder's RecordReader cache was a weak-identity map keyed on the reader Schema:

private final Map<Schema, Map<Schema, RecordReader>> readerCache =
    Collections.synchronizedMap(new WeakIdentityHashMap<>());

However, each cached RecordReader holds a strong reference to that same reader Schema (RecordReader.schema, needed by its InstanceSupplier at read time — getNewRecordSupplier returns this::newRecord, which takes the schema as a parameter). Because the cached value strongly references its own weak key, the weak entries can never be reclaimed. The cache therefore grows without bound whenever many distinct Schema instances are used — e.g. when a schema is re-parsed for every file or message in a long-running process — leading to unbounded memory growth (reports of caches reaching 100GB).

This is the memory leak tracked by AVRO-4253 (and its duplicate AVRO-3524). Note the earlier commit referencing AVRO-4253 (#3764) actually addressed an unrelated logging concern; the leak itself was still present.

How was this patch fixed?

Replace the weak two-level map with a bounded LRU cache keyed on an identity-based (reader, writer) schema pair:

• Bounds memory unconditionally, independent of the value-references-key cycle.
• Identity-based key preserves the original cache semantics and avoids the cost of Schema.equals/hashCode on large schemas.
• Recursion-safe: entries that are still INITIALIZING are never evicted, so recursive schema resolution still terminates by resolving back to the same in-flight instance instead of rebuilding endlessly.
• Evicting a cached reader is safe for in-use readers: the caller holds the returned DatumReader directly, so eviction only means a future lookup rebuilds it.
• The bound defaults to 2048 and is configurable via the org.apache.avro.fastreader.recordReaderCacheSize system property.

How was this patch tested?

New TestFastReaderBuilderCacheBounded:

• cacheStaysBoundedAcrossDistinctSchemaInstances — 3048 freshly-parsed (distinct-identity) schemas leave the cache bounded at <= 2048 (fails on the old unbounded code).
• reusedSchemaInstanceHitsCache — a reused schema instance keeps a single cache entry (cache still effective).
• recursiveSchemaReadsCorrectly — a self-referential (linked-list) schema round-trips correctly.

Also verified no regressions across the read path: TestResolvingIO (816), TestResolvingIOResolving (192), TestGenericDatumReader, TestGenericData, TestDataFile, TestResolver, and the FastReaderBuilder tests all pass under the default, custom-coders, and without-fast-reader surefire profiles.