Ack chunks after the flash write on the inflate path and harden the decoder

Chunk acks again mean the block is in flash on both paths: the read callback
writes and acks everything decoded so far before it waits for more input.
The decoder rejects a negative distance symbol, initialises its whole state,
and the flush feeds the watchdog once per window. The static_assert on the
backend skips the static analysis build, which sets every define at once.

tests/integration/test_host_ota.py

@@ -186,7 +186,7 @@ async def test_host_ota_self_update(
         if "OTA staged at" in line:
             staged.set()
         # The host backend has no gzip support, so the upload negotiates deflate
-        if "Inflated " in line:
+        if " bytes from " in line:
             inflated.set()
         dev.on_log(line)