Use the process CPU count to determine how many children to create

Python 3.13+ introduced os.process_cpu_count() which is better
aligned with want we want here

https://docs.python.org/3/library/os.html#os.process_cpu_count

Additionally this avoids bring in multiprocessing which
increases the startup time

reduction in `importtime-waterfall esphome.__main__`

```
        multiprocessing (82)
          multiprocessing.context (188)
            multiprocessing.process (221)
              signal (195)
            multiprocessing.reduction (116)
              pickle (293)
                struct (45)
                  _struct (209)
                _compat_pickle (101)
                _pickle (241)
              socket (405)
                _socket (320)
                array (205)
```

esphome/core/config.py

@@ -1,5 +1,4 @@
 import logging
-import multiprocessing
 import os
 from pathlib import Path
 
@@ -94,10 +93,15 @@ def valid_project_name(value: str):
     return value
 
 
+def get_usable_cpu_count() -> int:
+    return (
+        os.process_cpu_count() if hasattr(os, "process_cpu_count") else os.cpu_count()
+    )
+
+
 if "ESPHOME_DEFAULT_COMPILE_PROCESS_LIMIT" in os.environ:
     _compile_process_limit_default = min(
-        int(os.environ["ESPHOME_DEFAULT_COMPILE_PROCESS_LIMIT"]),
-        multiprocessing.cpu_count(),
+        int(os.environ["ESPHOME_DEFAULT_COMPILE_PROCESS_LIMIT"]), get_usable_cpu_count()
     )
 else:
     _compile_process_limit_default = cv.UNDEFINED
@@ -156,7 +160,7 @@ CONFIG_SCHEMA = cv.All(
             ),
             cv.Optional(
                 CONF_COMPILE_PROCESS_LIMIT, default=_compile_process_limit_default
-            ): cv.int_range(min=1, max=multiprocessing.cpu_count()),
+            ): cv.int_range(min=1, max=get_usable_cpu_count()),
         }
     ),
     validate_hostname,

script/clang-format

@@ -1,7 +1,6 @@
 #!/usr/bin/env python3
 
 import argparse
-import multiprocessing
 import os
 import queue
 import re
@@ -11,7 +10,13 @@ import threading
 
 import click
 import colorama
-from helpers import filter_changed, get_binary, git_ls_files, print_error_for_file
+from helpers import (
+    filter_changed,
+    get_binary,
+    get_usable_cpu_count,
+    git_ls_files,
+    print_error_for_file,
+)
 
 
 def run_format(executable, args, queue, lock, failed_files):
@@ -25,7 +30,9 @@ def run_format(executable, args, queue, lock, failed_files):
             invocation.extend(["--dry-run", "-Werror"])
         invocation.append(path)
 
-        proc = subprocess.run(invocation, capture_output=True, encoding="utf-8")
+        proc = subprocess.run(
+            invocation, capture_output=True, encoding="utf-8", check=False
+        )
         if proc.returncode != 0:
             with lock:
                 print_error_for_file(path, proc.stderr)
@@ -45,7 +52,7 @@ def main():
         "-j",
         "--jobs",
         type=int,
-        default=multiprocessing.cpu_count(),
+        default=get_usable_cpu_count(),
         help="number of format instances to be run in parallel.",
     )
     parser.add_argument(
@@ -80,7 +87,8 @@ def main():
         lock = threading.Lock()
         for _ in range(args.jobs):
             t = threading.Thread(
-                target=run_format, args=(executable, args, task_queue, lock, failed_files)
+                target=run_format,
+                args=(executable, args, task_queue, lock, failed_files),
             )
             t.daemon = True
             t.start()
@@ -95,7 +103,7 @@ def main():
         # Wait for all threads to be done.
         task_queue.join()
 
-    except FileNotFoundError as ex:
+    except FileNotFoundError:
         return 1
     except KeyboardInterrupt:
         print()
@@ -103,7 +111,7 @@ def main():
         # Kill subprocesses (and ourselves!)
         # No simple, clean alternative appears to be available.
         os.kill(0, 9)
-        return 2    # Will not execute.
+        return 2  # Will not execute.
 
     return len(failed_files)
 

script/clang-tidy

@@ -1,7 +1,6 @@
 #!/usr/bin/env python3
 
 import argparse
-import multiprocessing
 import os
 import queue
 import re
@@ -19,6 +18,7 @@ from helpers import (
     filter_changed,
     filter_grep,
     get_binary,
+    get_usable_cpu_count,
     git_ls_files,
     load_idedata,
     print_error_for_file,
@@ -170,7 +170,7 @@ def main():
         "-j",
         "--jobs",
         type=int,
-        default=multiprocessing.cpu_count(),
+        default=get_usable_cpu_count(),
         help="number of tidy instances to be run in parallel.",
     )
     parser.add_argument(

script/helpers.py

@@ -188,3 +188,14 @@ def get_binary(name: str, version: str) -> str:
             """
         )
         raise
+
+
+def get_usable_cpu_count() -> int:
+    """Return the number of CPUs that can be used for processes.
+
+    On Python 3.13+ this is the number of CPUs that can be used for processes.
+    On older Python versions this is the number of CPUs.
+    """
+    return (
+        os.process_cpu_count() if hasattr(os, "process_cpu_count") else os.cpu_count()
+    )