hmon: use single Arc for heartbeat monitor

[arkjedrz]

Replace previous approach with two Arcs.

[github-actions]

License Check Results

🚀 The license check job ran with the Bazel command:

bazel run --lockfile_mode=error //:license-check

Status: ⚠️ Needs Review

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[License Check Output]
Extracting Bazel installation...
Starting local Bazel server (8.6.0) and connecting to it...
INFO: Invocation ID: 5a5a848c-dff8-450d-af5a-cd0e7ef8c998
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Analyzing: target //:license-check (164 packages loaded, 7434 targets configured)

Analyzing: target //:license-check (164 packages loaded, 7434 targets configured)

Analyzing: target //:license-check (164 packages loaded, 7434 targets configured)

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Analyzing: target //:license-check (168 packages loaded, 10283 targets configured)

Analyzing: target //:license-check (168 packages loaded, 10283 targets configured)

Analyzing: target //:license-check (168 packages loaded, 10283 targets configured)

Analyzing: target //:license-check (168 packages loaded, 10283 targets configured)

INFO: Analyzed target //:license-check (169 packages loaded, 10409 targets configured).
[14 / 16] [Prepa] JavaToolchainCompileBootClasspath external/rules_java+/toolchains/platformclasspath.jar
[15 / 16] Building license.check.license_check.jar (); 0s disk-cache, multiplex-worker
INFO: Found 1 target...
Target //:license.check.license_check up-to-date:
  bazel-bin/license.check.license_check
  bazel-bin/license.check.license_check.jar
INFO: Elapsed time: 27.491s, Critical Path: 2.31s
INFO: 16 processes: 12 internal, 3 processwrapper-sandbox, 1 worker.
INFO: Build completed successfully, 16 total actions
INFO: Running command line: bazel-bin/license.check.license_check ./formatted.txt <args omitted>
usage: org.eclipse.dash.licenses.cli.Main [-batch <int>] [-cd <url>]
       [-confidence <int>] [-ef <url>] [-excludeSources <sources>] [-help] [-lic
       <url>] [-project <shortname>] [-repo <url>] [-review] [-summary <file>]
       [-timeout <seconds>] [-token <token>]

[github-actions]

The created documentation from the pull request is available at: docu-html

[danth]

Previously, calling get_eval_handle a second time for the same monitor would return a new handle with a separate timestamp. After this change, the same timestamp is shared between all handles.

I'm not sure what the expected behaviour should be, but it would be good to add a test for this either way.