Bump smartthings-local floor to 0.1.8

Two releases landed since the 0.1.6 pin, both confirmed by upstream
(QuiteYellow, in issue #361) as additive/opt-in with no interface
changes on our side:

- 0.1.7: server-certificate profiles (SamsungServerProfile), a bounded
  DTLS handshake deadline (connect() now defaults to a 12s bound
  instead of none), and a cancellable connect() via
  ConnectCancellation. Our connect() call sites in coordinator.py and
  config_flow.py pass no args, so they pick up the bounded handshake
  for free; the cert-profile and cancellation pieces are opt-in and
  unused here.

- 0.1.8: fixes blockwise OBSERVE notification reassembly
  (QuiteYellow/SmartThings-Local#39) -- a notification carrying only
  the first Block2 block was previously handed straight to
  on_notification instead of being reassembled, and separately, the
  Block2 loop could append a retransmitted/late block as if it were
  the next one, or miscompute the next block offset after a mid-
  transfer size downshift. Both corrupt a multi-block observed
  resource without necessarily truncating it -- the "premature end of
  stream" / "error decoding unicode string" CBOR failures reported in
  issue #361 on /mode/vs/0. All error types stay within the existing
  compatible-built-in table (ConnectionError/TimeoutError subclasses),
  so no exception handling changes.

`>=0.1.6` already permitted pip to resolve 0.1.8 on a fresh install,
but an environment that already has 0.1.6 or 0.1.7 satisfying that
floor won't be upgraded by Home Assistant's requirement check -- which
is what #361's reporter is very likely still hitting on 0.22.0.
Raising the floor to >=0.1.8 forces that upgrade on the next release.

Verified against smartthings-local 0.1.8 from PyPI: full suite (1573
tests), ruff, and ty all pass. No source changes needed beyond the
three version pins (manifest.json, requirements-dev.txt, Dockerfile).

Dockerfile

@@ -6,4 +6,4 @@ FROM ghcr.io/home-assistant/home-assistant:stable
 # repeats the install attempt on every container recreate. Baking
 # smartthings-local into the image keeps the dev container usable
 # offline and avoids relying on that runtime install path.
-RUN pip3 install --no-cache-dir "smartthings-local>=0.1.6"
+RUN pip3 install --no-cache-dir "smartthings-local>=0.1.8"

custom_components/localthings/manifest.json

@@ -11,7 +11,7 @@
   "requirements": [
     "cbor2>=5.4.6",
     "pyOpenSSL>=23.0",
-    "smartthings-local>=0.1.6"
+    "smartthings-local>=0.1.8"
   ],
   "version": "0.22.0"
 }

requirements-dev.txt

@@ -6,7 +6,7 @@ pytest-homeassistant-custom-component>=0.13.316
 
 # Integration runtime deps, needed to import the component under test
 # (also declared in custom_components/localthings/manifest.json).
-smartthings-local>=0.1.6
+smartthings-local>=0.1.8
 cbor2>=5.4.6
 pyOpenSSL>=23.0
 cryptography>=41.0