fix: don't wait on a log lock holder that can't run

The log lock is a binary semaphore, so when the radio task preempted loop()
mid-log every log from async_tcp waited the full 20ms for a holder that
couldn't let go until the radio job ended.  Waiting now stops as soon as
the holder is preempted on another core.  The rule lives in
LogLockPolicy.h with unit tests.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/LogLockPolicy.h

@@ -0,0 +1,21 @@
+#ifndef LOG_LOCK_POLICY_H
+#define LOG_LOCK_POLICY_H
+#include <stdint.h>
+
+// When a log call stops waiting for the log lock (src/LogLock.cpp).  Kept free
+// of FreeRTOS so it can be unit tested on the PC (pio test -e native).
+
+// What the task holding the log lock is doing.
+enum class LogHolder {
+  unknown,            // Just took the lock and hasn't recorded itself yet.
+  running,            // Running on a core, so it lets go within a line.
+  preemptedHere,      // Waiting for this core, so blocking lets it finish.
+  preemptedElsewhere  // Preempted on another core (the radio task during a
+                      // whole transmission), so waiting gets nowhere.
+};
+// Whether to keep waiting after waitedMs.  Never past maxMs.
+inline bool keepWaitingForLogLock(LogHolder holder, uint32_t waitedMs, uint32_t maxMs) {
+  if(waitedMs >= maxMs) return false;
+  return holder != LogHolder::preemptedElsewhere;
+}
+#endif