fix(core): Resolve TypeScript strict mode and ES client API compatibility issues for v3.0.0

- Fix ES client v8+ API: use document/doc instead of body for index/update operations
- Add type assertions (as any) for ES client ILM, template, and search APIs
- Fix strict null checks with proper undefined handling (nullish coalescing)
- Fix MetricsCollector interface to match required method signatures
- Fix Logger.error signature compatibility in plugins
- Resolve TermsQuery type index signature conflict
- Remove sourceMap from tsconfig (handled by tsbuild with inlineSourceMap)

ts/core/errors/elasticsearch-error.ts

@@ -1,4 +1,5 @@
-import { ErrorCode, ErrorContext } from './types.js';
+import { ErrorCode } from './types.js';
+import type { ErrorContext } from './types.js';
 
 /**
  * Base error class for all Elasticsearch client errors

ts/core/errors/retry-policy.ts

@@ -1,4 +1,4 @@
-import { RetryConfig, RetryStrategy } from './types.js';
+import type { RetryConfig } from './types.js';
 import { ElasticsearchError } from './elasticsearch-error.js';
 
 /**