Feature/merge validate pipeline

[Shashankss1205]

Reference Issues/PRs

See also: feature/merge_load_data_source

pr-469 (branch: feature/merge_validate_pipeline)

It is built directly on top of:

1. pr-468 (feature/merge_load_data_source)
2. pr-466 (feature/data_management)
3. pr-463 (feature/remove-legacy-discovery-tools)

What does this implement/fix? Explain your changes.

This PR merges the standalone validate_pipeline tool directly into the instantiate_pipeline lifecycle:

• Removed validate_pipeline tool schema registration and routing logic from server.py.
• Because the core executor (executor.instantiate_pipeline) already runs the pipeline composition validator, calling instantiate_pipeline now automatically checks validity first. If validation fails, it returns detailed errors and suggestions rather than registering the invalid handle.
• Added a new unit test test_pipeline_composition_check under TestPipelineParamsValidation in tests/test_param_validation.py to confirm that trying to instantiate invalid compositions (e.g. chaining forecasters like ["NaiveForecaster", "ExponentialSmoothing"]) correctly triggers composition validation and fails gracefully with detailed diagnostics.

This helps maintain a lean, highly integrated, and failsafe developer API surface.

Does your contribution introduce a new dependency? If yes, which one?

No.

What should a reviewer concentrate their feedback on?

• Verify that make check returns completely green and that all 190 tests pass.
• Verify that instantiating an invalid pipeline properly outputs success: False along with the validation diagnostics.

Any other comments?

N/A

PR checklist

For all contributions

• I've added unit tests and made sure they pass locally (make check).
• I've added the tool to the online documentation in docs/source/.
• I've updated the existing example scripts or provided a new one to showcase how my tool works in examples/.