feat(server): Add on-demand heap profiling endpoints

[jan-auer]

Adds gated heap profiling to production builds using jemalloc's built-in sampling. Profiling is compiled in via a new profiling Cargo feature (enabled in release/CI builds, off for debug) and dormant at startup. It can be activated on demand via HTTP endpoints, which dump a symbolized gzipped pprof profile.

• Outputs symbolized pprof, so profiles are self-contained and analyzable with go tool pprof without shipping the binary separately.
• Endpoints are loopback-only (peer IP check), reachable via kubectl port-forward or an ephemeral debug container. Normal service/ingress traffic never presents a loopback peer, so no separate listener or auth are needed.
• Profile sampling rate is set to 512 KiB mean interval which has negligible steady-state overhead without the feature being active.
• By default, sampling never runs unless explicitly enabled via the endpoint.

[codecov]

Codecov Report

❌ Patch coverage is 56.73077% with 45 lines in your changes missing coverage. Please review.
✅ Project coverage is 87.20%. Comparing base (3a7b4eb) to head (ef5475c).

Files with missing lines	Patch %	Lines
objectstore-server/src/endpoints/profiling.rs	55.00%	45 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #522      +/-   ##
==========================================
- Coverage   87.44%   87.20%   -0.24%     
==========================================
  Files          86       87       +1     
  Lines       13892    13993     +101     
==========================================
+ Hits        12148    12203      +55     
- Misses       1744     1790      +46     

Components	Coverage Δ
Rust Backend	91.97% <56.73%> (-0.35%)	⬇️
Rust Client	80.07% <ø> (ø)
Python Client	88.51% <ø> (ø)

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.