⚡ Bolt: Cache remaining GCP Executions and Projects client wrappers

[JulienBreux]

💡 What: Cache the GCP client wrappers in internal/run/api/job/execution/execution.go and internal/run/api/project/client.go.
🎯 Why: Avoids recreating and authenticating client wrappers on every single request, which previously introduced a ~300ms bottleneck.
📊 Impact: Cuts TUI latency significantly when loading executions or selecting projects.
🔬 Measurement: Verified caching behavior and thread-safety with unit tests in internal/run/api/job/execution/execution_test.go and internal/run/api/project/project_test.go.

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PR created automatically by Jules for task 10519752892151848484 started by @JulienBreux

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