fix: preserve enclosing stream filter when using MockInputOutput

[paulbalandan]

Description

When a test uses MockInputOutput while it (or its base) also uses StreamFilterTrait, the mock's internal addStreamFilters() / removeStreamFilters() calls tore down the trait's STDOUT/STDERR filters and left them removed. Any CLI output produced after the MockInputOutput interaction (for example in tearDown()) then bypassed capture and leaked to the console.

MockInputOutput now snapshots the shared CITestStreamFilter state (filter presence and buffer) before attaching its own filters and restores it afterward, so an enclosing StreamFilterTrait keeps capturing once the mock is done. Adds CITestStreamFilter::hasOutputFilter() / hasErrorFilter() accessors and a regression test covering both the fwrite and input paths.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value (without duplication)
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide