Fix alias_module_function on JRuby

[trans]

Fixes the only failing test in the JRuby CI job (test/standard/test_uri.rb: private method 'hash_to_query' called for module URI), which has been red on main since at least #325.

Cause

• URI.hash_to_query is defined with alias_module_function :hash_to_query, :query, which calls alias_method and then module_function(new).
• On JRuby 10.1, the singleton method module_function(name) creates is public, but it turns private as soon as it's aliased again. CRuby keeps it public.
• Lemon aliases every method under test to wrap it for coverage, then aliases it back afterwards. So once the URI.hash_to_query test ran, the method was private, and the later Hash#to_uri test failed.

Normal callers don't hit this unless they re-alias the method, but anything that wraps methods the way Lemon does will.

Fix

alias_module_function now aliases the singleton method directly:

def alias_module_function(new, old)
  alias_method(new, old)
  return module_function(new) unless singleton_class.method_defined?(old)
  singleton_class.send(:alias_method, new, old)
end

That matches the documented contract ("alias a module function so the alias is also a module function"), and the result stays public on JRuby. If old isn't a module function, it falls back to module_function(new) exactly as before.

Testing

I reproduced this locally with JRuby 10.1.2.0, the version CI uses.

• A new test re-aliases the singleton method. It fails on JRuby without this fix and passes with it. The existing test now also checks that the instance alias is private.
• Full suite on JRuby 10.1.2: 1,253 tests, 1,249 passing, 4 pending, 0 errors. Previously 1 error.
• Full suite on CRuby 3.3: the same, 0 errors.
• The fallback path (aliasing a plain instance method) behaves the same as before on both Rubies.

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https://claude.ai/code/session_01E2Njj4j1r9twkVcXsMySLW

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