Add half: keyword to Numeric#round

[znz]

Changes

Numeric#round is declared as () -> Integer | (Integer digits) -> Numeric, but it also accepts the half: keyword: numeric.c's num_round just calls flo_round(argc, argv, rb_Float(num)), so every argument is forwarded to Float#round, and the current rdoc call-seq is round(digits = 0, half: :up) -> integer or float.

• core/numeric.rbs: add ?half: round_mode to both overloads of Numeric#round (the round_mode alias is the one Integer#round already uses) and update the generated call-seq comment.
• test/stdlib/Numeric_test.rb: add test_round using a Numeric subclass that defines to_f, so the test exercises Numeric#round itself rather than Integer#round.

Measured on Ruby 4.0.7 with class N < Numeric; def to_f; 2.5; end; end:

N.new.round                 # => 3
N.new.round(half: :even)    # => 2
N.new.round(half: :down)    # => 2
N.new.round(1)              # => 2.5
N.new.round(1, half: :even) # => 2.5
N.new.round(0, half: :even) # => 2

Verification

• bin/test_runner.rb test/stdlib/Numeric_test.rb and rbs validate pass locally on Ruby 3.4.8.

🤖 Generated with Claude Code

[ksss]

@znz Thank you but,
We should update the Ruby version to v4.0.7 in comment CI.

[znz]

Thank you for the review. I looked at what the RBS Comments job actually rewrites: the only diff is the call-seq comment line that I had edited by hand (round(digits = 0, half: :up)). That line comes from ruby/ruby master (ruby/ruby@96311d13c2, "[DOC] Add missing half kwags to Numeric#round"), and the commit is in neither v4.0.7 nor the current ruby_4_0 branch, so the job would still regenerate round(digits = 0) after #3235.

I have dropped the hand edit and left the comment as generated; the signature and the test are unchanged. The comment can follow once a Ruby release used by the workflow carries that doc fix. The signature itself holds for 4.0.x: Numeric#round delegates to Float#round in every version, which accepts half:.

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