ToInt() previously wrapped strtol() with a nullptr endptr, so a failed
conversion was indistinguishable from a legitimate 0 (matching the old
TString::Atoi() behaviour). Switch the implementation to std::from_chars
and add an optional `bool *ok` out-parameter that reports success: it is
set to false on a non-numeric string or an out-of-range value, true
otherwise. Leading whitespace is skipped and trailing characters are
ignored, preserving the Atoi-like prefix semantics. The parameter
defaults to nullptr, so existing call sites keep compiling unchanged.
Convert the parse-validation call sites in PMsrHandler to the single
-parse ToInt(token, &ok) form, replacing the IsInt() guard + separate
ToInt() (which parsed every token twice). All downstream >0 / >=0 /
range / enum checks are preserved.
Left untouched the call sites where IsInt() acts as a structural
discriminator rather than a numeric validator (write path, xy-data
index-vs-label, fParamInUse usage scans) and the IsFloat-guarded ToInt
offsets, where switching to ToInt(&ok) would change parsing semantics.
All 85 integration tests pass.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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