feat: add snowflake grant support

[eakmanrq]

Adds support for Grants to Snowflake.

Also includes moving engine-adapter tests that should run for all engines that support grant to the test_integration.py folder and updating it to use patterns that are expected in that file (like creating test-specific objects instead of shared global objects).

[Copilot]

Pull Request Overview

This PR adds comprehensive grants support for Snowflake engine adapter, enabling database-level permission management through SQLMesh. The feature includes methods to sync grants configuration with the database, supporting common privileges like SELECT, INSERT, UPDATE for roles and users.

• Implements grants functionality for Snowflake engine adapter with sync and query methods
• Adds comprehensive test coverage for grants operations including edge cases
• Refactors integration tests to use shared grants testing utilities

Reviewed Changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
sqlmesh/core/engine_adapter/snowflake.py	Core implementation of grants support with sync and query methods
sqlmesh/core/engine_adapter/postgres.py	Minor type annotation fix for MAX_IDENTIFIER_LENGTH
sqlmesh/core/engine_adapter/risingwave.py	Explicitly disables grants support
sqlmesh/core/engine_adapter/_typing.py	Adds DCL type variable for grant/revoke operations
tests/core/engine_adapter/test_snowflake.py	Extensive unit tests for Snowflake grants functionality
tests/core/engine_adapter/integration/init.py	Shared utilities for creating users/roles in integration tests
tests/core/engine_adapter/integration/test_integration.py	Generic grants integration tests
tests/core/engine_adapter/integration/test_integration_postgres.py	Refactored to use shared test utilities
.circleci/continue_config.yml	Temporary CI configuration changes

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