Define explicit ownership for custom appenders and formatters

Add SharedLogState for synchronized value data and factories for
independently owned appender state and captured formatter closures.
Reject unsafe configuration state, update the test collector to value
snapshots, and document the breaking APIs in version 3.0.0.

Expand ORC ownership and sanitizer coverage and reject stale test
executables.

tests/runtime_allocator.nim

@@ -0,0 +1,38 @@
+## Standalone reproduction of Nim 2.2.10's allocator sanitizer report.
+## No logging-library imports. All accesses to the shared sequence hold a lock.
+import std/[atomics, locks]
+
+type AllocatorData = object
+  lock: Lock
+  entries: seq[int]
+  total: int
+
+var start: Atomic[bool]
+
+proc withData(data: ptr AllocatorData,
+    action: proc(entries: var seq[int]) {.gcsafe.}) =
+  withLock data.lock:
+    action(data.entries)
+    inc data.total
+
+proc append(data: ptr AllocatorData, value: int) =
+  data.withData(proc(entries: var seq[int]) =
+    entries.add(value)
+    if entries.len >= 64: entries = @[])
+
+proc worker(data: ptr AllocatorData) {.thread.} =
+  while not start.load(): discard
+  for i in 0 ..< 10_000: data.append(i)
+
+proc runAllocatorRegression*() =
+  var data: AllocatorData
+  initLock(data.lock)
+  defer: deinitLock(data.lock)
+  var workers: array[4, Thread[ptr AllocatorData]]
+  for thread in workers.mitems: createThread(thread, worker, addr data)
+  start.store(true)
+  joinThreads(workers)
+  doAssert data.total == 40_000
+
+when isMainModule:
+  runAllocatorRegression()