* Support onSchemaChange for incremental tables

This change introduces support for the onSchemaChange option in incremental tables for the BigQuery adapter. It adds the incrementalSchemaChangeBody() strategy to handle schema changes.

End-to-end tests have been created to verify the new functionality.

* fix: Private functions moved after public functions

* - Split onSchemaChange queries to sub-tasks
- Split sql queries to sun-functions
- Fixed function names

* fix: Address feedback for PR #2101 and fix presubmit failures

- Updated e2e tests - Added golden files - Consolidated merge and insert functions

- Add `jit_code` field to the `Assertion` message in `protos/core.proto`
- Fix missing protobuf imports and configuration in `protos/BUILD`
- Introduce `JitAssertionResult` type alias and `jitCode` method to `Assertion` builder (`core/actions/assertion.ts`)
- Add strictly typed `jitContextable` parameter to `Session.sqlxAction` in `core/session.ts`
- Update assertion `compile()` to handle `jitCode` execution bypassing standard string evaluation
- Parse and apply `jitContextable` safely for assertions in `core/session.ts`
- Add unit test coverage in `core/main_test.ts` to verify compilation output

- extend onSchemaChange e2e test timeout (#2175)