vehicle_time: Deliver VehicleClock callbacks from a worker thread

[florianfueller]

Improvement

Description

Implement callback delivery in VehicleClockBackendImpl; the Set*/Unset* methods were
no-ops so far.

• A worker thread, started by the first successful Init(), polls the TimeDaemon shared
  memory every 50 ms while at least one callback is registered and dispatches on that thread.
• TimeSlaveSyncData / PDelayMeasurementData fire on every changed frame.
• VehicleTimeStatus fires once after registration, then only when the flags change
  (rate deviation excluded).
• Subscribe / Unsubscribe are safe against in-flight invocations, including calls from
  inside a callback.
• Unit tests added; docs and comments updated, "not yet delivered" warnings removed.

Related ticket

closes #59 (improvement ticket)

[github-actions]

License Check Results

🚀 The license check job ran with the Bazel command:

bazel run //:license-check

Status: ⚠️ Needs Review

Click to expand output

[License Check Output]
Extracting Bazel installation...
Starting local Bazel server (8.6.0) and connecting to it...
INFO: Invocation ID: 27726e0f-cf1f-4a35-a9a8-92314acab12f
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
WARNING: For repository 'platforms', the root module requires module version platforms@1.0.0, but got platforms@1.1.0 in the resolved dependency graph. Please update the version in your MODULE.bazel or set --check_direct_dependencies=off
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Computing main repo mapping: 
Loading: 
Loading: 3 packages loaded
Analyzing: target //:license-check (4 packages loaded, 0 targets configured)
Analyzing: target //:license-check (4 packages loaded, 0 targets configured)

Analyzing: target //:license-check (72 packages loaded, 10 targets configured)

Analyzing: target //:license-check (109 packages loaded, 449 targets configured)

Analyzing: target //:license-check (157 packages loaded, 3160 targets configured)

Analyzing: target //:license-check (164 packages loaded, 6259 targets configured)

Analyzing: target //:license-check (169 packages loaded, 6308 targets configured)

Analyzing: target //:license-check (169 packages loaded, 6308 targets configured)

Analyzing: target //:license-check (169 packages loaded, 6308 targets configured)

Analyzing: target //:license-check (172 packages loaded, 8195 targets configured)

Analyzing: target //:license-check (175 packages loaded, 11421 targets configured)

Analyzing: target //:license-check (176 packages loaded, 11429 targets configured)

Analyzing: target //:license-check (176 packages loaded, 11429 targets configured)

Analyzing: target //:license-check (176 packages loaded, 11429 targets configured)

INFO: Analyzed target //:license-check (177 packages loaded, 11555 targets configured).
[12 / 16] JavaToolchainCompileClasses external/rules_java+/toolchains/platformclasspath_classes; 0s disk-cache, processwrapper-sandbox ... (2 actions running)
INFO: From Generating Dash formatted dependency file ...:
INFO: Successfully converted 2 packages from Cargo.lock to bazel-out/k8-fastbuild/bin/formatted.txt
[14 / 16] JavaToolchainCompileBootClasspath external/rules_java+/toolchains/platformclasspath.jar; 0s disk-cache, processwrapper-sandbox
[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: 33.734s, Critical Path: 2.70s
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>]