fix: grant cap_sys_resource to the shim, log $PATH on setcap failure

[ilmanzo]

Summary

• cilium/ebpf's rlimit.RemoveMemlock() is a no-op on kernels with memcg-based BPF memory accounting (the norm on kernel >=6.6, required here), but its own accounting-support probe can misfire under BPF memory pressure and fall back to raising RLIMIT_MEMLOCK, which requires CAP_SYS_RESOURCE. Without it that fallback hard-fails the whole tracer instead of the no-op it's meant to be (observed: curl's shim exiting before exec'ing real curl with remove memlock: operation not permitted).
• Adds cap_sys_resource to the shim's capability set in setShimCaps as cheap, low-risk insurance against that fallback path — scoped to the shim binary via file capabilities, used for exactly one Prlimit call.
• Also logs $PATH alongside setcap failures, to help root-cause a separate class of "setcap: executable file not found in $PATH" failures seen in some coverage runs.

Test plan

• go build ./... and go vet ./... pass
• ./run_unit_tests.sh passes
• Verified live against a real openQA coverage run with the new capability applied and the PATH diagnostic firing as expected
• Note: in the run where this was tested, the actual root cause of the curl_https failure turned out to be a missing libcap-progs test-infra dependency (fixed separately, out of scope for this repo) rather than the capability gap this PR closes — but the extra capability and diagnostic logging are still worth keeping as defense-in-depth once setcap itself is working.

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 43.73%. Comparing base (10d21a8) to head (f2f3603).
⚠️ Report is 2 commits behind head on main.
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Additional details and impacted files

@@           Coverage Diff           @@
##             main     #131   +/-   ##
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  Coverage   43.73%   43.73%           
=======================================
  Files          11       11           
  Lines        1525     1525           
=======================================
  Hits          667      667           
  Misses        762      762           
  Partials       96       96           

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