fix: recognize all ASCII whitespace

[nightcityblade]

Summary

Complete ASCII whitespace classification with vertical tab and form feed, and reuse it from trimming.

Motivation

Fixes #591.

Target and compatibility impact

All targets now consistently recognize the six ASCII whitespace bytes.

Validation

• target/debug/wavec check tests/cases/shared/test81.wave
• git diff --check
• The full run was attempted but this macOS environment lacks ld64.lld.

Checklist

• Commits include a DCO Signed-off-by line.
• Tests cover new behavior or the PR explains why no test is needed.
• User-facing changes include documentation or diagnostics updates.
• The change preserves the license boundary between the compiler and std/.

[LunaStev]

LGTM thanks