Fix comment loss and misplacement in match arms, nested records, and raw strings

[xav-ie]

Description of changes

Fixes three formatter bugs that silently lose or misplace comments, several of which also make formatting non-idempotent (running the formatter repeatedly keeps changing the file). Each has a ground-truth + idempotency fixture.

1. Parenthesized match-arm guards vacuum nearby comments into (

A match arm with a parenthesized guard (pat if (EXPR) => body) pulled surrounding standalone comments inside the guard's (:

# before
match $x {
  a => 1
  # a comment between arms
  b if ($y | foo) == 'z' => 2
}
# after (buggy)
match $x {
    a => 1
    b if (
# a comment between arms
$y | foo) == 'z' => 2
}

The guard is rendered in a probe_format sub-formatter whose comment cursor was reset to the start of file, so the parenthesized sub-expression re-flushed every not-yet-written comment. Fix: seed each arm's probe with the pattern's own start position, and emit arm-preceding comments at the arm boundary in format_match_block (a bare guard if $y == 'z' previously dropped the same comment entirely).

2. Nested records collapse inline and drop field comments

# before
$env.config = {
  trim: {
    # wrapping or truncating
    methodology: wrapping
  }
}
# after (buggy)  ->  comment gone, inner record collapsed
$env.config = {
  trim: {methodology: wrapping}
}

The record layout decision only preserved source newlines at the top level and never checked for comments, so a short nested record took the inline path — which emits fields without write_comments_before. Fix: force multiline when the record span contains comments, using the same has_comments_in_span guard format_list already applies.

3. r#'…'# raw strings derail comment extraction

A raw string with hash delimiters containing # caused extract_comments to mis-lex: the # in r#' started a bogus comment and the closing '# opened a phantom string that swallowed real comments until the next stray apostrophe — deleting ~1 comment per pass (non-idempotent). Fix: teach extract_comments to skip r#'…'# (and multi-hash variants) and consume each quoted string inline so an unterminated string can't bleed across the file; single-quoted strings are treated as raw (no backslash escapes).

Testing

cargo test — full suite green (273 tests, incl. 7 new fixtures). All three cases verified idempotent.

Relevant Issues

None found open; happy to file tracking issues if preferred.

[fdncred]

Thanks