Mixed-case underscore Python exclusions retain incorrectly cased paths

[n0tl3ss]

PR #1915 review5434888907 identifies an inconsistent Python filename normalization guard. MacroUtils normalizes Hello_Controller to hello_controller, but GuideProjectGenerator and GuideAsciidocGenerator return early whenever a name contains an underscore. That affects flat test exclusions as well as packaged main/test paths.

Regressions were added first for actual generated-project exclusions and lowercase controls. The first macOS filesystem run masked the defect because the filesystem is case-insensitive. Strengthening that same regression with exact string assertions for both private project helpers and the Asciidoc main/test paths reproduces the bug independently of filesystem casing: the focused seven-test run has one failing mixed-case regression; the cache-input fix and remaining controls pass. Actual generation and retained-file sentinels remain checked.

The shared fix belongs in prerequisite #1914: remove the underscore early-return in both existing normalization guards, leaving lowercase identifiers unchanged. No new API, abstraction, native build or language-enablement change is needed. Normally merge into #1915.

[n0tl3ss]

Removing only the underscore shortcut from the two existing guards makes the exact-case path assertions and actual generation/exclusion controls pass. The lowercase identifiers and retained-file controls continue to pass. Complete shared-infrastructure validation executes 156 tests with zero failures/errors/skips and all 16 Python project/script tasks execute successfully. No API widening or helper abstraction was added. Changes will be published as a new prerequisite #1914 commit, then normally merged into draft #1915.