fix: _save no longer resolves the store's realpath twice per call

_save() already resolves target = realpath(self.file) for the write path;
_sweep_stale_tmp then independently recomputed the same realpath to derive its
match basename. _sweep_stale_tmp now takes that resolved basename as a
parameter instead of re-resolving it, cutting one syscall per save. the sweep
itself still runs on every save (unchanged) - gating it to first-save-per-
instance would change when a crash-orphaned tmp from before this process
started actually gets swept, so that part is left alone.

Signed-off-by: disqualifier <dev@disqualifier.me>

src/aiokv/aiokv.py

@@ -121,7 +121,7 @@ class AioKV:
         target = await asyncio.to_thread(os.path.realpath, self.file)
         directory = os.path.dirname(target) or "."
         await asyncio.to_thread(os.makedirs, directory, exist_ok=True)
-        await self._sweep_stale_tmp(directory)
+        await self._sweep_stale_tmp(directory, os.path.basename(target))
 
         payload = await asyncio.to_thread(json.dumps, cache, allow_nan=False)
         tmp = f"{target}.{os.getpid()}.tmp"
@@ -137,14 +137,15 @@ class AioKV:
                     log.exception("aiokv: failed to clean up temp file %s", tmp)
             raise
 
-    async def _sweep_stale_tmp(self, directory: str) -> None:
+    async def _sweep_stale_tmp(self, directory: str, base: str) -> None:
         """remove orphaned .<pid>.tmp files left by a hard crash of a different, dead process
 
         matches only the exact shape _save() creates (<realpath basename>.<pid>.tmp), via a
         re.escape'd regex over a directory listing rather than a raw glob - a glob pattern
         both crosses unrelated dots (matching non-aiokv neighbors like foo.backup.999.tmp) and
-        mistreats glob metacharacters in the store's own filename (e.g. state[prod].json)"""
-        base = os.path.basename(await asyncio.to_thread(os.path.realpath, self.file))
+        mistreats glob metacharacters in the store's own filename (e.g. state[prod].json).
+        `base` is the realpath'd basename _save() already resolved - passed in rather than
+        re-resolved here so a save does one realpath call, not two."""
         candidate = re.compile(rf"^{re.escape(base)}\.(\d+)\.tmp$")
         names = await asyncio.to_thread(os.listdir, directory)
         for name in names: