refactor: drop three orphaned private symbols

Dead code surfaced by an unused-symbol sweep across `packages/`:

- `_BRANCHES` (repl/_indent.py): a frozenset that was only there
  to document which Robot keywords (`ELSE`, `ELSE IF`, `EXCEPT`,
  `FINALLY`) the indent counter ignores. Replaced with a short
  inline comment — same self-documenting effect, no orphan symbol.
- `_split_comma` (analyze/code/cli.py): a click callback added
  alongside the `--xm` / `--xe` exit-code-mask options, then
  superseded by `_parse_exit_code_mask` and never wired up.
- `_cancel_all_running_tasks` (core/concurrent.py): originally
  the public `cancel_running_callables`; the FutureEx → Task
  rename privatised it but no caller followed.

Author: d-biehl

packages/analyze/src/robotcode/analyze/code/cli.py

@@ -138,15 +138,6 @@ def _parse_exit_code_mask(ctx: click.Context, param: click.Option, value: Tuple[
         raise click.BadParameter(str(e)) from e
 
 
-def _split_comma(ctx: click.Context, param: click.Option, value: Optional[List[str]]) -> List[str]:
-    if value is None:
-        return []
-    result: List[str] = []
-    for item in value:
-        result.extend([x.strip() for x in item.split(",") if x.strip()])
-    return result
-
-
 def _validate_load_library_timeout(ctx: click.Context, param: click.Option, value: Optional[int]) -> Optional[int]:
     """Validate --load-library-timeout (>0) or pass through None."""
     if value is None:

packages/core/src/robotcode/core/concurrent.py

@@ -10,7 +10,6 @@
     Dict,
     Generic,
     Iterator,
-    List,
     Optional,
     Protocol,
     Tuple,
@@ -255,15 +254,3 @@ def run_as_debugpy_hidden_task(callable: Callable[_P, _TResult], *args: _P.args,
     thread.start()
 
     return future
-
-
-def _cancel_all_running_tasks(timeout: Optional[float] = None) -> None:
-    threads: List[threading.Thread] = []
-    with _running_tasks_lock:
-        for future, thread in _running_tasks.items():
-            if not future.cancelation_requested:
-                future.cancel()
-                threads.append(thread)
-    for thread in threads:
-        if thread is not threading.current_thread():
-            thread.join(timeout=timeout)

packages/repl/src/robotcode/repl/_indent.py

@@ -29,12 +29,10 @@
 # Closer — pops one level of indent.
 _CLOSERS = frozenset({"END"})
 
-# Branch markers stay at the *current* depth — they don't open or
-# close a block, but they live inside one. Tracking them isn't
-# strictly necessary for the indent counter (they're net-zero), but
-# we keep the constant for clarity and to make it obvious why the
-# counter doesn't touch them.
-_BRANCHES = frozenset({"ELSE", "ELSE IF", "EXCEPT", "FINALLY"})
+# Branch markers (`ELSE`, `ELSE IF`, `EXCEPT`, `FINALLY`) are net-zero
+# for the depth counter — they live inside an open block but neither
+# open nor close one. The counter ignores them by default; no
+# enumeration needed.
 
 _DEFAULT_WIDTH = 4