Integration-test hardening + bootstrap race tolerance + XML docs

[bfarmer67]

Summary

Two scope-distinct improvements bundled per the established release cadence (v2.2.1):

Dispatcher / integration-test hardening (commit 5563b5e):

• StatementDispatcher: pass CAS query params (if_seq_no/if_primary_term) via IRequestParameters instead of embedding them in the path string (OpenSearch.Net rejects embedded query strings); add CasPutParameters.
• Handle OpenSearchClientException in DispatchUpdateSettingsAsync and DispatchReindexAsync for ThrowExceptions=true clients.
• SafeDefaultMergeMiddleware: co-inject conflicts: proceed with op_type: create on REINDEX to prevent abort-on-conflict defeating idempotency (ADR-0011).
• R-24c gap-fill tests: handle both ThrowExceptions modes; defensive cleanup against container-teardown races.
• InitializeTestContainers: HYPERBEE_TESTS_PROVIDERS_ONLY env gate to scope startup; HYPERBEE_TESTS_SKIP_SINGLE_NODE support.
• CouchbaseTestContainer: remove erroneous port 80 mapping.

Public-surface gap closure (commit 2528250):

• LedgerIndexInitStep / LockIndexInitStep: tolerate the TOCTOU race between Exists() and Create() by detecting resource_already_exists_exception in both client modes. Ledger step still verifies the existing mapping on race-loss.
• OpenSearchMigrationOptions: full XML docs on every public type, enum value, property, const, and ctor; lift R-19 / R-29 / PA-2 rationale from line comments into <summary>/<remarks>; add <see cref> links between related options.
• OpenSearchExceptions: full XML docs on every exception type and ctor.

Test plan

• Provider builds clean: 0 warnings, 0 errors across net8/net9/net10.
• Unit tests: 356/356 pass on net10.
• Integration tests (non-MultiNode OpenSearch suite): 75/75 pass across all 3 frameworks.
• Multi-node OpenSearch tests: not run locally (Docker resource constraints — 3 JVMs); CI handles via R-28b multi_node_tests.yml.