Make an ignore-file pattern matcher follow its spec (anchoring, directory-only, double-star, negation, parent exclusion)

# Make the ignore-file matcher follow its spec `ignore.py` decides which paths our sync tool skips, using `.gitignore`-style patterns. It is a quick `fnmatch` hack and gets many cases wrong. Rewrite it so `Matcher(text).ignored(path, is_dir=False)` follows the rules below exactly. Python 3 standard library only. Keep the class name, constructor and method signature. `path` is a relative POSIX path with no leading `./` or `/` (e.g. `src/app/main.py`); `is_dir` says whether the path itself is a directory. Every ancestor of `path` (e.g. `src`, `src/app`) is a directory. ## Rules 1. **Lines.** Split `text` into lines (strip a trailing `\r`). Trailing spaces are removed unless the last space is escaped as `\ ` (backslash-space, which keeps one literal space). Blank lines are ignored. A line starting with `#` is a comment; `\#` at the start is a literal `#`. Leading spaces are NOT stripped. 2. **Negation.** A leading `!` makes the pattern a negation (re-include). `\!` at the start is a literal `!`. 3. **Directory-only.** A trailing `/` is removed and makes the pattern match only directories. A pattern that is empty after removing `!` and the trailing `/` is ignored. 4. **Anchoring.** If the remaining pattern contains a `/` anywhere (start or middle), it is matched against the full path from the root (a leading `/` is dropped first). Otherwise it is matched against the last component at any depth (i.e. against the full path or any suffix that starts right after a `/`). 5. **Wildcards.** `*` matches any run of characters except `/` (including none); `?` matches exactly one character except `/`. `[...]` is a character class: ranges like `a-z` work, `!` or `^` as the first character negates it, a `]` directly after `[` (or after the negation mark) is literal; a class never matches `/`. A `[` with no closing `]` is a literal `[`. A backslash outside a class makes the next character literal. 6. **Double star.** Only these forms are special: a leading `**/` matches zero or more leading directories; `/**/` matches one `/` or `/any/dirs/`; a trailing `/**` matches one or more characters (anything inside, but not the directory itself). Any other run of `*` (e.g. `a**b`, `**` on its own) behaves like a single `*`. 7. **Last match wins.** For a given path, look at all patterns in file order; the last one that matches decides (normal = ignored, negated = not ignored). No match = not ignored. Directory-only patterns are only considered when the path being tested is a directory. 8. **Parents.** First test each ancestor directory from the top (`src`, then `src/app`, ...) using rule 7 with `is_dir=True`. If any ancestor is ignored, the path is ignored and nothing (not even a later `!` pattern) can re-include it. Otherwise the path's own result from rule 7 is the answer. 9. **Speed.** Building a matcher from 300 patterns and answering 20,000 `ignored()` calls must take under 10 seconds in total on our (shared, slow) test box. ## Scoring Hidden checks (one per group, all must pass; partial credit is the fraction passed): `comments_spaces_escapes` (rules 1-2, 5 backslash), `negation_last_match` (2, 7), `dir_only` (3, 7), `anchoring` (4), `wildcards_classes` (5), `double_star` (6), `parent_exclusion` (8), `randomized_agreement` (400 random pattern/path pairs built from the characters `a b / * ? [ ] ! -` must all agree with the rules), `speed` (9). Each group has 10-40 exact assertions.