SchemaView performance improvements

[rschili]

itwinjs-core: iTwin/itwinjs-core#9431

New schema view fragment pragma that will be used by iTwinjs-core to load just subsets of an iModels' schema.
Plus a few fixes, please read the linked itwinjs-core PR description and issue for full details.

[rschili]

@khanaffan are you okay with this change?
The previous code was logging a warning because pragma going through concurrent query does not have those two parameters.
This change makes it so we don't log those warnings anymore.
Unrelated change, sneaking it in because it's small and insignificant.

[Copilot]

Pull request overview

This PR extends ECDb’s ECSQL pragma surface to support incremental SchemaView loading (fragments) for iTwinjs-core, and introduces a cheap schema identity hash (schema_token) intended for cache invalidation and determinism checks.

Changes:

• Add PRAGMA schema_view_fragment(...) to return a subset of schemas as a SchemaView-format blob for incremental loading.
• Add PRAGMA checksum(schema_token) backed by a new “name+version only” schema identity hash, and align schema_view’s schemaToken with it.
• Refactor/extend SchemaViewWriter to support fragment filtering and safer state reuse; reduce noisy parameter-missing logs in concurrent query limit binding.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
iModelCore/ECDb/Tests/NonPublished/ECSqlPragmasTests.cpp	Updates checksum/token assertions and adds coverage for schema_token and schema_view_fragment behavior.
iModelCore/ECDb/ECDb/SchemaViewWriter.h	Adds fragment-related API/state and clarifies non-concurrent instance usage.
iModelCore/ECDb/ECDb/SchemaViewWriter.cpp	Implements fragment filtering, request validation, centralized reset, and safer narrowing for serialized fields.
iModelCore/ECDb/ECDb/ECSql/ECSqlPragmas.h	Extends checksum docs/options and declares schema_view_fragment + schema-token hashing support.
iModelCore/ECDb/ECDb/ECSql/ECSqlPragmas.cpp	Implements checksum(schema_token), shared schema_view row building, and schema_view_fragment argument parsing.
iModelCore/ECDb/ECDb/ECDbImpl.cpp	Registers the new schema_view_fragment pragma handler.
iModelCore/ECDb/ECDb/ConcurrentQueryManagerImpl.cpp	Uses TryGetParameterIndex to avoid log spam when LIMIT/OFFSET params don’t exist (e.g., PRAGMAs).