Fix crash on an endless method with empty parentheses (#361)

[youdie006]

Fixes #361.

Problem

Formatting a shorthand (endless) method definition with empty parentheses crashes:

def foo() = 1

Rufo::Bug: Expected token on_int, not on_sp

def foo(x) = 1, def foo = 1, and non-endless def foo() all format fine — it is specific to the empty-parens-plus-endless combination.

Cause

In visit_def_from_name, the empty-parameters branch writes "()" but, unlike the two sibling branches (non-empty parens and the no-parens elsif), does not skip_space after consuming the closing parenthesis. So the endless-method check format_endless_method if current_token_kind == :on_op sees the space (:on_sp) before = instead of the = operator, skips format_endless_method, and visit body then hits the unconsumed = 1, raising Rufo::Bug.

Fix

Add skip_space after write "()", mirroring the sibling branches.

Test

Added two cases to spec/lib/rufo/formatter_source_specs/endless_methods.rb.spec (def foo() = 1 idempotent, and def foo() = 1 normalized to def foo() = 1). Red-green verified with rspec: both raise Rufo::Bug before the fix and format correctly after; the full formatter spec (977 examples) passes and rubocop is clean.

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Disclosure: prepared with AI assistance (Claude); I reviewed it and verified the red-green spec and the full formatter suite.