Use `platformdirs` for `.config.get_app_dir()`

Replace hand-rolled `click`-based platform branching using
the much saner `platformdirs.user_config_path()`.

Deats,
- remove Windows/macOS/Unix `if/elif` platform dispatch
  (~25 lines) in favour of single `user_config_path()` call.
- move `_posixify()` inside `force_posix` branch since it's
  only used there.
- add `log.info()` reporting platform name and resolved dirs.

Also,
- drop now unneeded `sys` import.
- reformat `assert` in `repodir()` to multiline style.
- convert docstring from `r"""..."""` to `'''...'''` style.

(this commit msg was generated in some part by [`claude-code`][claude-code-gh])
[claude-code-gh]: https://github.com/anthropics/claude-code

piker/config.py

@@ -19,7 +19,6 @@ Platform configuration (files) mgmt.
 
 """
 import platform
-import sys
 import os
 import shutil
 from typing import (
@@ -29,6 +28,7 @@ from typing import (
 from pathlib import Path
 
 from bidict import bidict
+import platformdirs
 import tomlkit
 try:
     import tomllib
@@ -41,7 +41,7 @@ from .log import get_logger
 log = get_logger('broker-config')
 
 
-# XXX NOTE: taken from `click`
+# XXX NOTE: orig impl was taken from `click`
 # |_https://github.com/pallets/click/blob/main/src/click/utils.py#L449
 #
 # (since apparently they have some super weirdness with SIGINT and
@@ -54,44 +54,21 @@ def get_app_dir(
     force_posix: bool = False,
 
 ) -> str:
-    r"""Returns the config folder for the application.  The default behavior
+    '''
+    Returns the config folder for the application.  The default behavior
     is to return whatever is most appropriate for the operating system.
 
-    To give you an idea, for an app called ``"Foo Bar"``, something like
-    the following folders could be returned:
+    ----
+    NOTE, below is originally from `click` impl fn, we can prolly remove?
+    ----
 
-    Mac OS X:
-      ``~/Library/Application Support/Foo Bar``
-    Mac OS X (POSIX):
-      ``~/.foo-bar``
-    Unix:
-      ``~/.config/foo-bar``
-    Unix (POSIX):
-      ``~/.foo-bar``
-    Win XP (roaming):
-      ``C:\Documents and Settings\<user>\Local Settings\Application Data\Foo``
-    Win XP (not roaming):
-      ``C:\Documents and Settings\<user>\Application Data\Foo Bar``
-    Win 7 (roaming):
-      ``C:\Users\<user>\AppData\Roaming\Foo Bar``
-    Win 7 (not roaming):
-      ``C:\Users\<user>\AppData\Local\Foo Bar``
-
-    .. versionadded:: 2.0
-
-    :param app_name: the application name.  This should be properly capitalized
-                     and can contain whitespace.
     :param roaming: controls if the folder should be roaming or not on Windows.
                     Has no affect otherwise.
     :param force_posix: if this is set to `True` then on any POSIX system the
                         folder will be stored in the home folder with a leading
                         dot instead of the XDG config home or darwin's
                         application support folder.
-    """
-
-    def _posixify(name):
-        return "-".join(name.split()).lower()
-
+    '''
     # NOTE: for testing with `pytest` we leverage the `tmp_dir`
     # fixture to generate (and clean up) a test-request-specific
     # directory for isolated configuration files such that,
@@ -117,23 +94,30 @@ def get_app_dir(
     #         assert testdirpath.exists(), 'piker test harness might be borked!?'
     #         app_name = str(testdirpath)
 
-    if platform.system() == 'Windows':
-        key = "APPDATA" if roaming else "LOCALAPPDATA"
-        folder = os.environ.get(key)
-        if folder is None:
-            folder = os.path.expanduser("~")
-        return os.path.join(folder, app_name)
+    os_name: str = platform.system()
+    conf_dir: Path = platformdirs.user_config_path()
+    app_dir: Path = conf_dir / app_name
+
+    # ?TODO, from `click`; can remove?
     if force_posix:
+        def _posixify(name):
+            return "-".join(name.split()).lower()
+
         return os.path.join(
-            os.path.expanduser("~/.{}".format(_posixify(app_name))))
-    if sys.platform == "darwin":
-        return os.path.join(
-            os.path.expanduser("~/Library/Application Support"), app_name
+            os.path.expanduser(
+                "~/.{}".format(
+                    _posixify(app_name)
+                )
+            )
         )
-    return os.path.join(
-        os.environ.get("XDG_CONFIG_HOME", os.path.expanduser("~/.config")),
-        _posixify(app_name),
+
+    log.info(
+        f'Using user config directory,\n'
+        f'platform.system(): {os_name!r}\n'
+        f'conf_dir: {conf_dir!r}\n'
+        f'app_dir: {conf_dir!r}\n'
     )
+    return app_dir
 
 
 _click_config_dir: Path = Path(get_app_dir('piker'))
@@ -250,7 +234,9 @@ def repodir() -> Path:
         repodir: Path = Path(os.environ.get('GITHUB_WORKSPACE'))
         confdir: Path = repodir / 'config'
 
-    assert confdir.is_dir(), f'{confdir} DNE, {repodir} is likely incorrect!'
+    assert confdir.is_dir(), (
+        f'{confdir} DNE, {repodir} is likely incorrect!'
+    )
     return repodir