feat: bound PSS/E dynamic output responses

[BurhanAbdullah]

Summary

Follow up on #97 to bound the size of read_dynamic_output MCP responses.

Changes

• Add a safe default cap of 10,000 time points.
• Add max_points so callers can request a tighter response bound.
• Apply deterministic, evenly spaced, endpoint-preserving sampling when the source exceeds the cap.
• Preserve time-series/channel alignment by validating that all returned channels match the time-vector length.
• Return num_points, total_points, downsampled, and the effective max_points so callers can see exactly how the response was handled.
• Reject invalid max_points values before starting the PSS/E engine.
• Update the PSS/E README with the new response-cap behavior.
• Add regression coverage for explicit caps, the default cap, endpoint preservation, invalid inputs, and pre-engine validation.

Validation

The new tests use the existing fake dyntools path, so they do not require a licensed PSS/E installation.

This addresses the follow-up from #97: an unbounded request for all dynamic-output channels can otherwise produce an unnecessarily large MCP response.