chore: switch to ruff + pydoclint, deprecate .gitingest, and perform a repo-wide quality sweep (#329)

* **Pre-commit**: replace `black` & `darglint` with `ruff-check` / `ruff-format`;
  add `pydoclint` for docstring quality
* **Deps**: drop `tomli`; tighten `typing_extensions`; add `eval-type-backport`;
  remove `black`, `djlint`, `pylint` from `requirements-dev`
* **Ignore files**: deprecate TOML-based `.gitingest`; introduce
  `.gitingestignore` (git-wildmatch, parsed via `_parse_ignore_file`)
* **Config**: new unified `[tool.ruff]` (lint + format + isort); delete
  `[tool.black]`, keep minimal `[tool.isort]` for now
* **Refactor/style**: adopt `from __future__ import annotations`, kw-only args,
  richer types; reorder params & `__all__`; move type-only imports under
  `if TYPE_CHECKING`; extract `_CLIArgs` `TypedDict`, migrate form data to
  `pydantic.QueryForm`; deduplicate `cli.main` / `_async_main`; use `pathlib`,
  avoid file-IO in async; replace magic numbers with constants; delete
  `is_text_file` (logic now lives in `FileSystemNode.content`)
* **Bug fix**: remove silent error in `notebook_utils._process_cell`
* **Docs**: refresh README badges
* **Tests**: update fixtures & assertions

**BREAKING**: new `.gitingestignore` file replaces (now-deprecated) `.gitingest`.

No functional API or CLI changes.

.pre-commit-config.yaml

@@ -38,11 +38,6 @@ repos:
       - id: absolufy-imports
         description: "Automatically convert relative imports to absolute. (Use `args: [--never]` to revert.)"
 
-  - repo: https://github.com/psf/black
-    rev: 25.1.0
-    hooks:
-      - id: black
-
   - repo: https://github.com/asottile/pyupgrade
     rev: v3.20.0
     hooks:
@@ -79,12 +74,18 @@ repos:
         description: "Lint markdown files."
         args: ["--disable=line-length"]
 
-  - repo: https://github.com/terrencepreilly/darglint
-    rev: v1.8.1
+  - repo: https://github.com/astral-sh/ruff-pre-commit
+    rev: v0.12.0
     hooks:
-      - id: darglint
-        name: darglint for source
-        args: [--docstring-style=numpy]
+      - id: ruff-check
+      - id: ruff-format
+
+  - repo: https://github.com/jsh9/pydoclint
+    rev: 0.6.7
+    hooks:
+      - id: pydoclint
+        name: pydoclint for source
+        args: [--style=numpy]
         files: ^src/
 
   - repo: https://github.com/pycqa/pylint
@@ -104,7 +105,6 @@ repos:
             slowapi,
             starlette>=0.40.0,
             tiktoken,
-            tomli,
             pathspec,
             uvicorn>=0.11.7,
           ]
@@ -124,7 +124,6 @@ repos:
             slowapi,
             starlette>=0.40.0,
             tiktoken,
-            tomli,
             pathspec,
             uvicorn>=0.11.7,
           ]