feat: Add C bindings for DynamoDB Big Segments store

[beekld]

Summary

Adds a C binding for DynamoDBBigSegmentStore so C callers can wire the existing DynamoDB Big Segments integration into the SDK's Big Segments config.

New public surface:

• LDServerBigSegmentsDynamoDBStore opaque handle.
• struct LDServerBigSegmentsDynamoDBResult with store and error_message fields.
• LDSERVER_BIGSEGMENTS_DYNAMODBSTORE_ERROR_MESSAGE_SIZE macro.
• LDServerBigSegmentsDynamoDBStore_New(table_name, prefix, options, out_result) factory.
• LDServerBigSegmentsDynamoDBStore_Free(store).

Tests:

• Unit tests for successful creation with and without the options builder (NULL means "AWS SDK default provider chain").
• End-to-end test against DynamoDB Local: primes a sync timestamp via PrefixedDynamoDBClient::PutBigSegmentSyncTime, wires the store through the C API, and verifies the SDK reports the store available via the Big Segment status listener.

The type name uses config-section-first word order (BigSegments + DynamoDB + Store), matching the sibling Redis Big Segments binding LDServerBigSegmentsRedisStore (#574) and the sibling DynamoDB LazyLoad binding LDServerLazyLoadDynamoDBSource (#576). The options parameter reuses the LDServerDynamoDBClientOptionsBuilder introduced in #576.

Stacked on #576 (DynamoDB LazyLoad source). Please review that PR first.

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Note

Low Risk
New public C surface and binding glue only; core Big Segments DynamoDB logic is unchanged and risk is limited to ownership/error-handling in the thin wrapper.

Overview
Exposes the existing DynamoDB Big Segments integration to C callers via a new public header and thin C++ shim, following the same patterns as the Redis Big Segments and DynamoDB LazyLoad C bindings.

The API adds LDServerBigSegmentsDynamoDBStore_New / _Free, a result struct with a fixed-size error_message buffer, and optional LDServerDynamoDBClientOptionsBuilder (consumed on success; NULL uses the AWS default provider chain). The implementation delegates to DynamoDBBigSegmentStore::Create and documents wiring through LDServerBigSegmentsBuilder and LDServerConfigBuilder_BigSegments.

Build wiring adds bindings/dynamodb/dynamodb_big_segment_store.cpp to the dynamodb-source library. Tests cover creation with and without options, plus a DynamoDB Local end-to-end path that seeds Big Segments sync metadata and asserts the SDK Big Segment store status listener reports available.

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