Fix RBS rewriting to preserve line numbers

[Morriar]

Fixes #787

Problem

When using Spoom::Sorbet::Translate.rbs_comments_to_sorbet_sig, line numbers weren't preserved. Multi-line RBS comments were replaced with single-line sigs, causing method definitions to shift up in the file. This made errors and stacktraces misalign with the original source.

Example:

# Original (method at line 6)
#: (
#| Integer
#| ) -> void
def foo(i); end

# After translation (method moved to line 4)
sig { params(i: Integer).void }
def foo(i); end

Solution

Added a preserve_line_numbers helper that:

1. Calculates how many lines the original RBS comment spans
2. Calculates how many lines the generated sig will have
3. Adds blank lines after the sig to match the original line count

Result:

# After fix (method stays at line 6)
sig { params(i: Integer).void }


def foo(i); end

Testing

• All existing tests pass
• Updated test_translate_to_rbi_multiline_sigs to expect preserved line numbers
• Manually tested with various RBS comment sizes (single-line, multi-line, complex signatures)

Changes

• lib/spoom/sorbet/translate/rbs_comments_to_sorbet_sigs.rb:
  • Added preserve_line_numbers helper method
  • Updated rewrite_def to use line preservation
  • Updated visit_attr to use line preservation
• test/spoom/sorbet/translate/rbs_comments_to_sorbet_sigs_test.rb:
  • Updated test_translate_to_rbi_multiline_sigs expectations

[paracycle]

What happens if original_lines < replacement_lines? Could that ever happen? Should we handle that explicitly and raise if that is not expected?