Fix quoted tokens and comment handling

[git-hulk]

Problem

The lexer splits escaped quoted identifiers, silently turning "a""b"
into column "a" with alias "b". It classifies dollar-quoted strings
as identifiers, stops nested block comments at the first closing marker,
and rejects supported hash comments.

Reproduction

SELECT "a""b";
SELECT $$hello$$;
SELECT /* outer /* inner */ outer */ 1;
SELECT 1 # comment

The first two produce incorrect ASTs; the last two fail parsing.

Fix

Handle doubled delimiters and backslash escapes in identifiers, normalize
complete dollar strings into the existing escaped string representation,
and track block-comment depth. Recognize # and #! comments through
LF or EOF, matching ClickHouse's lexer.

Keep unmatched named dollar delimiters as identifiers, as ClickHouse does.
Escape literal line breaks so beautification preserves string values.
No exported types or fields are added.

Test

• Lexer regressions cover token kind, escaped spelling, source positions,
  following separators, and formatting/reparsing. Quoted-identifier,
  dollar-string, and nested-comment cases failed before the lexer fix.
• Extend invalid-input, error-position, and comment-termination tests.
  Add an AST and compact/beautified SQL fixture.
• ClickHouse local 26.7.1.1315: 29 valid inputs produce matching ASTs for
  all 58 compact/beautified outputs; both engines reject nine invalid cases.
• make test (race and compatibility tests), make lint, and make
  pass with Go 1.21.13. Tests/lint use external linking on macOS.