Fix: chain reformatting leaves multi-line arguments orphaned

[sorafujitani]

Summary

When reformat_chain_lines (PR #100's aligned → indented rewrite) fires on a multi-line method chain that contains a call with multi-line arguments such as .select(...), only the .method lines get moved. Anything inside the call's argument list — strings split across lines, the trailing ), etc. — stays at its original column:

# before
@users = User.left_joins(articles: :article_likes)
             .group('users.id')
             .select(
               'users.*, ' \
               'COUNT(CASE WHEN articles.status = 1 THEN article_likes.id END) AS received_likes_count'
             )
             .having('received_likes_count > 0')

# after (bug)
@users = User.left_joins(articles: :article_likes)
  .group('users.id')
  .select(
               'users.*, ' \
               'COUNT(CASE WHEN articles.status = 1 THEN article_likes.id END) AS received_likes_count'
             )
  .having('received_likes_count > 0')

The chain body sits at column 6 but the .select(...) arguments still float at column 15, and the closing ) lands at column 13 — visually orphaned and trailing off to the right.

Root cause

reformat_chain_lines rewrites every .method line to " " * (base_indent + indent_width) but preserves every non-chain continuation line as-is. When the original chain sat at a deeper indent than the new one (aligned → indented is always this direction), anything aligned relative to the original chain — function arguments, closing parens, etc. — is left stranded.

Fix

Before rewriting, capture the original chain indent (the leading whitespace of the first .method line) and compute arg_shift = original_chain_indent − new_chain_indent. For every non-chain continuation line whose leading indent is at or deeper than the original chain indent, shift its leading whitespace by arg_shift. Lines shallower than the original chain indent — a squiggly-heredoc body measured against its own terminator, for instance — are left alone so we don't eat through their content.

# after (this PR)
@users = User.left_joins(articles: :article_likes)
  .group('users.id')
  .select(
    'users.*, ' \
    'COUNT(CASE WHEN articles.status = 1 THEN article_likes.id END) AS received_likes_count'
  )
  .having('received_likes_count > 0')

Regression tests

spec/chain_multiline_args_spec.rb (3 cases):

• multi-line .select(...) args shift with the chain
• no-op when there is no chain reformat (paren-only call)
• heredoc body indent is preserved when the chain reformat applies to a tail .squish/.strip etc.

Test plan

• cargo test --manifest-path ext/rfmt/Cargo.toml --lib — 127 passed
• bundle exec rspec — 134 passed (131 existing + 3 new)
• cargo clippy -- -D warnings — clean
• cargo fmt --check — clean
• bundle exec rubocop — clean
• All 50 Rails-idiom fixtures from earlier sweeps remain idempotent