[Continuing Discussion] `python_no_test_files` directive

This is a continuation of the discussion from https://github.com/bazelbuild/rules_python/pull/1819#discussion_r1542543260.

# 🚀 feature request

### Relevant Rules

+ gazelle

### Description

The summary of the discussion in https://github.com/bazelbuild/rules_python/pull/1819#discussion_r1542543260 so far is:

+ Having `python_test_file_pattern` accept no value is unintuitive and should raise an error. #1819 includes this.
+ Setting `python_test_file_pattern` back to "default" should be done manually, not through magic strings.
+ Eg: `# gazelle:python_test_file_pattern *_test.py,test_*.py`
+ There's still not a _nice_ way to tell gazelle that there are _no files in the bazel package_ that should be mapped to `py_test` targets _but should still be processed as py_library or py_binary_ (see example below).
+ Workaround: set `python_test_file_pattern` to a value that ends in something other than `.py`, such as `gazelle:python_test_file_pattern ignore_me.txt`. This will work because a prior check ([here](https://github.com/bazelbuild/rules_python/blob/5631f05024ec02e04d2b9c74a93b06f934cbfac6/gazelle/python/generate.go#L108) and [here](https://github.com/bazelbuild/rules_python/blob/5631f05024ec02e04d2b9c74a93b06f934cbfac6/gazelle/python/generate.go#L179)) asserts that the files being processed by gazelle end in `.py`.
+ All of the above led to the conclusion that there should be a `python_no_test_files` directive.

```
# example of project structure
project/
+ BUILD.bazel
+ MODULE.bazel
+ src/mypackage/ # guaranteed to have no py_test targets
+ BUILD.bazel
+ run_electrical_test.py # py_binary
+ electrical_test.py # py_library
+ tests/ # will have any py_* targets
+ BUILD.bazel
+ foo_test.py # py_test
+ bar_test.py # py_test
+ test_utils.py # py_library
+ run_all_test.py # py_binary
```

How does `python_no_test_files` behave? Does it:

1. cause gazelle to simply _ignore_ all files that match `python_test_file_pattern`? or
2. cause gazelle to map all files that match `python_test_file_pattern` to `py_library` or `py_binary` (if they have `if __name__ ...`)?

### Describe the solution you'd like

With behavior (1), there's still a feature gap for the example case above, and the workaround feels a bit hacky.

For behavior (2) we'd probably want to name the directive something else.

### Describe alternatives you've considered

Using `python_ignore_files` and then manually generating the py_library targets for files that match `python_test_file_pattern`. This is less than ideal when adding things to large projects.

Bắt đầu bằng việc đọc cuộc thảo luận được liên kết về pull request #1819, sau đó kiểm tra gazelle/python/generate.go tại các phép kiểm tra được tham chiếu quanh dòng 108 và 179. Issue cần có hành vi và tên directive được quyết định trước khi có thể xác định phạm vi triển khai; hoàn tất nghĩa là Gazelle xử lý các package không có target py_test mà không cần workaround đã được tài liệu hóa.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.