utils: add flamegraph for heap profiles

[erikgrinaker]

Problem

Unlike CPU profiles, the /profile/heap endpoint can't automatically generate SVG flamegraphs. This requires the user to install and use pprof tooling, which is unnecessary and annoying.

Resolves #10203.

Summary of changes

Add format=svg for the /profile/heap route, and generate an SVG flamegraph using the inferno crate, similarly to what pprof-rs already does for CPU profiles.

[github-actions]

7095 tests run: 6798 passed, 0 failed, 297 skipped (full report)

---

Flaky tests (3)

Postgres 17

• test_subscriber_synchronous_commit: release-x86-64
• test_timeline_archival_chaos: release-arm64

Postgres 15

• test_lr_with_slow_safekeeper: release-arm64

Code coverage* (full report)

• functions: 31.2% (8400 of 26887 functions)
• lines: 47.9% (66689 of 139118 lines)

* collected from Rust tests only

---

_{The comment gets automatically updated with the latest test results
96908ef at 2024-12-22T22:37:53.271Z :recycle:}