fix: only treat the last path segment as a filename in path()

isFilePath() checked the entire path for a dot to decide whether path() was given
a file or a directory. Because the path includes the location and name, a dot in
a parent segment (for example a location like /tmp/my.app) caused a directory
argument to be misclassified as a file, so the requested subdirectory was not
created. Inspect only the last path segment instead.

PR.md

@@ -0,0 +1,74 @@
+# fix: only treat the last path segment as a filename in path()
+
+## Problem
+
+`TemporaryDirectory::path()` fails to create a requested subdirectory when the
+temporary directory's location contains a dot:
+
+```php
+$tmp = (new Spatie\TemporaryDirectory\TemporaryDirectory('/tmp/my.app'))
+    ->name('run1')
+    ->create();
+
+$path = $tmp->path('abc');   // "abc" is a directory
+is_dir($path);               // false  <-- the directory was not created
+```
+
+`path('abc')` is documented and tested to create the `abc` subdirectory (see
+`it_can_create_a_subdirectory_in_the_temporary_directory`), but here it returns a
+path whose directory does not exist.
+
+## Root cause
+
+`src/TemporaryDirectory.php`. `path()` decides whether the argument points to a
+file (create only the parent directory) or a directory (create the whole path)
+via `isFilePath()`:
+
+```php
+protected function isFilePath(string $path): bool
+{
+    return str_contains($path, '.');
+}
+```
+
+`$path` is the full path (`location + name + argument`), so the check reacts to a
+dot anywhere in it - including a dot in the location such as `/tmp/my.app`. When
+that happens, a directory argument like `abc` is misclassified as a file, and
+`removeFilenameFromPath()` strips the `abc` segment, so only the already existing
+parent is created and `abc` is skipped.
+
+## The fix
+
+Only the last path segment can be a filename, so inspect just that segment:
+
+```php
+protected function isFilePath(string $path): bool
+{
+    $lastSeparator = strrpos($path, DIRECTORY_SEPARATOR);
+    $lastSegment = $lastSeparator === false ? $path : substr($path, $lastSeparator + 1);
+
+    return str_contains($lastSegment, '.');
+}
+```
+
+A dot in a parent segment (the location or name) no longer affects the
+file/directory decision, while a real filename such as `test.txt` in the last
+segment is still detected.
+
+## Test
+
+Added `it_can_create_a_subdirectory_when_the_location_contains_a_dot`, which
+creates a temporary directory under a location containing dots and asserts that
+`path('abc')` actually creates the `abc` directory.
+
+## Gate
+
+```
+composer install && vendor/bin/phpunit
+```
+
+Result: exit code `0` - `OK (23 tests, 37 assertions)`.
+
+Counterfactual: reverting `isFilePath()` to `str_contains($path, '.')` makes the
+new test fail - `Failed asserting that directory
+"/tmp/my.dotted.location/temporary_directory/abc" exists`.