feat(minor): Add signposts for explicit starts

[hassila]

Description

Adding support for per-iteration signposts as requested in
#259

How Has This Been Tested?

Manually verified.

Minimal checklist:

• I have performed a self-review of my own code
• I have added DocC code-level documentation for any public interfaces exported by the package
• I have added unit and/or integration tests that prove my fix is effective or that my feature works

[codecov]

Codecov Report

Attention: Patch coverage is 90.47619% with 2 lines in your changes missing coverage. Please review.

Project coverage is 65.32%. Comparing base (f03eaa2) to head (69e56e4).

Files	Patch %	Lines
Sources/Benchmark/Benchmark.swift	80.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #260      +/-   ##
==========================================
+ Coverage   65.30%   65.32%   +0.01%     
==========================================
  Files          33       33              
  Lines        3597     3610      +13     
==========================================
+ Hits         2349     2358       +9     
- Misses       1248     1252       +4     

Files	Coverage Δ
Sources/Benchmark/BenchmarkExecutor.swift	90.73% <100.00%> (+0.28%)	⬆️
Sources/Benchmark/Benchmark.swift	66.98% <80.00%> (-2.63%)	⬇️

Files	Coverage Δ
Sources/Benchmark/BenchmarkExecutor.swift	90.73% <100.00%> (+0.28%)	⬆️
Sources/Benchmark/Benchmark.swift	66.98% <80.00%> (-2.63%)	⬇️

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[github-actions]

Pull request had an unknown failure
Pull request benchmark comparison [ubuntu-latest] with 'main' run at 2024-08-13T10:00:45+00:00