Add goroutine leak profile to `ipfs diag profile`

Go 1.26 ships an experimental goroutine leak profiler (GOEXPERIMENT=goroutineleakprofile). It detects goroutines blocked on channels, mutexes, or conditions that can never unblock, using GC reachability analysis. Zero runtime overhead unless actively collecting.

Available at /debug/pprof/goroutineleak when enabled.

Proposal

Once 1.27 ships with it enabled by default:

• Add a goroutine-leak collector to ipfs diag profile --collectors (gated on the experiment being available at runtime)
• Expose it via the existing /debug/pprof/ endpoint on the API port

This would help diagnose daemon goroutine leaks without external tooling. Useful for long-running nodes where leaked goroutines accumulate over time.

References

• https://go.dev/doc/go1.26#goroutineleak-profiles
• runtime/pprof goroutineleak profile
• Expected to be enabled by default in Go 1.27