[client-v2] Implement a framework for schema validation

### Description

There are common case in integration connectors to validate record schema against a target table schema.
Today it is done like:
1. read list of tables
2. read table schema (using different approach)
3. cache these schema

No files, tests, or entry points are named. Start by locating the client-v2 integration and existing table-schema metadata paths, then clarify the validation API, supported schema sources, caching behavior, and connector scope. Done should include an agreed framework design and tests covering schema validation and cached target schemas.

Written by the indexing model from the issue text.