Fix clang-tidy findings in src/ (#1925)

[devtejasx]

Works through part of the collated clang-tidy list, restricted to changes that cannot alter behaviour:

• misc-const-correctness: declare locals const where they are never reassigned, spelling the qualifier first to match the surrounding code.
• readability-uppercase-literal-suffix: uppercase integer literal suffixes.
• readability-simplify-boolean-expr: distribute the negation in IsTruthyFlagValue() instead of negating a disjunction, and drop a manual counting loop in favour of the value it was recomputing.
• misc-use-anonymous-namespace: move the file-local console reporter helpers IgnoreColorPrint() and FormatTime() into an anonymous namespace rather than marking them static.

No functional change. Release and debug builds are clean and the test suite passes.

---

Per AGENTS.md: AI-assisted — the patch was drafted with AI assistance
(Claude) and then reviewed, tested, and understood by me. I take full
responsibility for it.

[dmah42]

did you consider why these checks aren't enabled?

[devtejasx]

I read the question as: the config globs them in, but that is not the same as the project wanting them applied. .clang-tidy does list misc-* and readability-*, and clang-tidy 20 reports six misc-const-correctness hits in complexity.cc alone — but WarningsAsErrors is empty and nothing runs it in CI, so the glob is a starting point for #1925 rather than a mandate.

So I have cut this down to the three findings that are not a matter of taste:

• 0u to 0U,
• two negated disjunctions distributed (RunInThread() and IsTruthyFlagValue()),
• the two file-local console reporter helpers moved from static into an anonymous namespace.

The misc-const-correctness batch, which was most of the previous diff, is gone. If what is left is still more churn than you want against #1925, say so and I'll close it.

[dmah42]

so maybe we should start by running clang-tidy on CI (or even on pre-commit) before we add more fixes. fwiw, i wouldn't care about u vs U. the anonymous namespace fix is nice.

[devtejasx]

Thanks for the feedback. It sounds like agreeing on clang tidy enforcement should come first, so I will close this PR for now. Once the project decides which checks to enforce, I can send focused cleanup patches that match that polic