feat: add runtime statistics tracking and integration tests for PluginStats

[LuigiGonnella]

📋 Summary

Add per-plugin runtime statistics to the Rhai plugin runtime. Introduces a thread-safe PluginStats struct to track total calls, failed calls, and cumulative latency, along with accessors and JSON snapshot support.

This enables monitoring plugin usage, debugging failures, and measuring performance in a production-ready way.

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🔗 Related Issues

Closes #235

Related to #173

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🧠 Context

Currently, Rhai plugins do not expose any runtime statistics, making it difficult to measure plugin performance, detect errors, or optimize execution.

This PR solves the problem by:

• Recording call counts and failures in AtomicU64 counters
• Measuring total latency and providing average latency calculations
• Exposing statistics safely to external callers via a stats() accessor
• Adding unit and integration tests to validate functionality

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🛠️ Changes

• Introduce PluginStats struct with counters, record(), avg_latency_ms(), and to_map()
• Attach PluginStats to RhaiPlugin and pub use it from rhai_runtime/mod.rs
• Add stats() accessor on RhaiPlugin returning Arc<PluginStats>
• Unit tests in crates/mofa-plugins/src/rhai_runtime/plugin.rs for counter increments, average latency, zero-call guard
• Integration test in crates/mofa-plugins/tests/rhai_integration_tests.rs driving plugin invocations and asserting stats

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🧪 How you Tested

1. Unit tests verify PluginStats counters increment correctly and average latency calculations
2. Integration test drives a sample plugin through multiple calls and validates stats snapshot
3. Verified thread-safety by simulating concurrent plugin calls (atomic counters)

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📸 Screenshots / Logs (if applicable)

N/A – metrics are exposed via JSON snapshot in tests

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⚠️ Breaking Changes

• No breaking changes
• Breaking change (describe below)

If breaking: N/A

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🧹 Checklist

Code Quality

• Code follows Rust idioms and project conventions
• cargo fmt run
• cargo clippy passes without warnings

Testing

• Tests added/updated
• cargo test passes locally without any error

Documentation

• Public APIs documented
• README / docs updated (if needed)

PR Hygiene

• PR is small and focused (one logical change)
• Branch is up to date with main
• No unrelated commits
• Commit messages explain why, not only what

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🚀 Deployment Notes (if applicable)

No migrations or config changes; rollout is safe.

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🧩 Additional Notes for Reviewers

• PluginStats uses AtomicU64 for thread-safety
• Zero-call guard ensures average latency doesn’t divide by zero
• Integration test demonstrates typical usage and snapshot reading

[LuigiGonnella]

@BH3GEI let me know