Remove dependency on irb

[Bo98]

Description

irb/notifier usage appears to just be debug logs that are never actually activated since they aren't linked up to YARD's own logging system.

The dependency on it therefore seems unnecessary and looks safe to remove, fixing compatibility with Ruby 4.0.

Normally this would only be a problem with the legacy parser but overload tag parsing still unconditionally uses the legacy parser only:

yard/lib/yard/tags/overload_tag.rb

Lines 58 to 60 in eddd10c

	# FIXME: refactor this code to not make use of the Handlers::Base class (tokval_list should be moved)
	toks = YARD::Parser::Ruby::Legacy::TokenList.new(args)
	args = YARD::Handlers::Ruby::Legacy::Base.new(nil, nil).send(:tokval_list, toks, :all)

Fixes #1636
Fixes #1645

Completed Tasks

• I have read the Contributing Guide.
• The pull request is complete (implemented / written).
• Git commits have been cleaned up (squash WIP / revert commits).
• I wrote tests and ran bundle exec rake locally (if code is attached to PR).