fix(test): pin monotonic clock in spinner-elapsed test to fix CI flake (#54203)

test_spinner_elapsed_format_is_fixed_width_to_reduce_wrap_jitter derived
_tool_start_time from the live time.monotonic() clock (now - 65.2 / now - 9.2).
monotonic()'s epoch is arbitrary — on a host where monotonic() < 65.2 (fresh
subprocess on a freshly-booted CI runner) the start time went negative, the
(t0 > 0) guard in _render_spinner_text() dropped the '(elapsed)' suffix, and
short.split('(',1)[1] raised IndexError: list index out of range. Deterministic
given a small clock, so it would keep flaking, not clear on rerun.

Pin time.monotonic to a fixed 1000.0 and offset _tool_start_time from it so both
the <60s and >=60s paths always render the elapsed suffix regardless of the
runner's monotonic epoch.

Pre-existing main flake (surfaced in CI test slice 1/8).

tests/cli/test_cli_status_bar.py

@@ -400,13 +400,20 @@ class TestCLIStatusBar:
         cli_obj = _make_cli()
         cli_obj._spinner_text = "running tool"
 
-        # <60s path
-        cli_obj._tool_start_time = time.monotonic() - 9.2
-        short = cli_obj._render_spinner_text()
+        # Pin the clock: time.monotonic()'s epoch is arbitrary (often near
+        # boot), so deriving _tool_start_time from the real monotonic clock
+        # made the test fail on hosts where monotonic() < 65.2 — the start
+        # time went negative, the (t0 > 0) guard in _render_spinner_text
+        # dropped the "(elapsed)" suffix entirely, and the split below hit an
+        # IndexError. A fixed clock keeps both elapsed paths deterministic.
+        with patch.object(cli_mod.time, "monotonic", return_value=1000.0):
+            # <60s path
+            cli_obj._tool_start_time = 1000.0 - 9.2
+            short = cli_obj._render_spinner_text()
 
-        # >=60s path
-        cli_obj._tool_start_time = time.monotonic() - 65.2
-        long = cli_obj._render_spinner_text()
+            # >=60s path
+            cli_obj._tool_start_time = 1000.0 - 65.2
+            long = cli_obj._render_spinner_text()
 
         short_elapsed = short.split("(", 1)[1].rstrip(")")
         long_elapsed = long.split("(", 1)[1].rstrip(")")