Investigate and enable azure-cosmos disabled tests

# Disabled Tests in azure-cosmos-tests

## Class-Level Disables (entire test class)

| # | Test Class | Reason |
|---|---|---|
| 1 | **`VectorIndexTest`** (all tests) | Waiting for public emulator with vector index support to be released |
| 2 | **`FullTextIndexTest`** (all tests) | Waiting for public emulator with full-text search support to be released |
| 3 | **`HybridSearchQueryTest`** (all tests) | Waiting for public emulator to be released |
| 4 | **`MalformedResponseTests`** (all tests) | Must run in isolation — uses Reflection to override the ObjectMapper instance for deserialization; unsafe in parallel test runs |

## Method-Level Disables (individual tests)

| # | Test Class | Test Method | Reason |
|---|---|---|---|
| 5 | **`CosmosConflictsTest`** | `conflictCustomLWW` | No reason given (`@Ignore` with no message) |
| 6 | **`SessionTest`** | `partitionedSessionToken` | TODO 32129 — flaky test, needs fix before re-enabling |
| 7 | **`AggregateQueryTests`** | `queryDocumentsWithAggregates` | TODO 32129 — flaky test, needs fix before re-enabling |
| 8 | **`GoneAndRetryPolicyWithSpyClientTest`** | `createRecoversFrom410GoneClientGeneratedOnPartitionSplitDuringIdleTime` | TODO 32129 — flaky test, needs fix before re-enabling |
| 9 | **`ChangeFeedTest`** | `changeFeed_incrementalOnFullFidelityContainer_fromNow` | Bug in emulator — always uses full-fidelity change feed on containers with retention |
| 10 | **`RequestHeadersSpyWireTest`** | `readItemWithCacheBypass` | Requires a SQLX endpoint to run (not available in standard test env) |
| 11 | **`JsonNodeStorePayloadTests`** | `parsingBytesWithInvalidUT8Bytes` | `fallbackCharsetDecoder` only initializes on first class load; no way to reload the class in-test |

## Summary by Category

- **Waiting for emulator features**: 3 classes (VectorIndex, FullText, HybridSearch)
- **Flaky / TODO 32129**: 3 tests (SessionTest, AggregateQuery, GoneAndRetry)
- **Environment-specific**: 2 tests (SQLX endpoint, isolation required)
- **Technical limitation**: 1 test (class reloading)
- **Emulator bug**: 1 test (ChangeFeed)
- **No reason documented**: 1 test (ConflictsTest)