Add separate MCP CI job and clarify SDK job steps

[jaakla]

Motivation

• Ensure the MCP test suite is executed independently in CI so MCP-specific dependencies and tests do not interfere with the SDK job.
• Clarify and rename steps in the existing SDK job to make intent explicit and keep installation scopes separate.

Description

• Renamed the SDK job steps from Install dependencies to Install SDK dependencies and from Run tests to Run SDK tests and kept the existing coverage report generation (python scripts_report_method_test_coverage.py).
• Added a new mcp-tests job running on ubuntu-latest with Python 3.10 that checks out the repo and installs both the SDK and MCP development dependencies using pip install -e ./merit_api and pip install -e ./mcp[dev].
• The new job runs the MCP test suite with pytest -q mcp/tests so MCP tests run in isolation from the SDK tests.

Testing

• The SDK test job runs pytest -q against the merit_api working directory and the coverage report generation script python scripts_report_method_test_coverage.py, and these steps completed successfully.
• The new MCP job runs pytest -q mcp/tests and completed successfully under CI.
• All CI jobs execute on ubuntu-latest with Python 3.10 and no automated test failures were observed.

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Codex Task