Fix namespace::clean stub missing get_functions and clean_subroutines

[dwright]

Inquisitor.pm stubs out namespace::clean to prevent it from wiping the symbol table before inspection:

$INC{'namespace/clean.pm'} = '';
*{'namespace::clean::import'} = sub { };

However, the stub only provides import and VERSION. Any module that calls namespace::clean->get_functions($package) or namespace::clean->clean_subroutines(...) as a class method at file scope — not inside a BEGIN block — will fail with:

Can't locate object method "get_functions" via package "namespace::clean"

This causes a cascade of BEGIN failed errors through the dependency chain, which perlnavigator surfaces as dozens of false Syntax error diagnostics in the editor — one per line of the stack trace — all pointing to line 1 of the file being checked.

Root Cause
The call to namespace::clean->get_functions(...) at file scope is valid Perl and works at runtime, because namespace::clean loads normally. But under -MInquisitor, the real namespace::clean is blocked from loading, and the stub doesn't provide a get_functions method.

Fix
Add a working get_functions stub that reads CODE symbols from the package stash directly — matching the real implementation's return value — and a no-op clean_subroutines stub:

*{'namespace::clean::get_functions'} = sub {
    my ($pragma, $class) = @_;
    no strict 'refs';
    return { map { $_ => \&{"${class}::${_}"} }
             grep { defined &{"${class}::${_}"} }
             keys %{"${class}::"} };
};
*{'namespace::clean::clean_subroutines'} = sub { };

The clean_subroutines stub is a safe no-op since symbol table cleanup is intentionally skipped during inspection anyway.

Tests
Added t/02_NamespaceClean.t with a regression test and testWorkspace/MyLib/NamespaceCleanCaller.pm as a fixture that calls namespace::clean->get_functions(__PACKAGE__) at file scope. All 6 tests pass.