Consolidate SSL ciphers and use them in SslTransport (#1798)

- Add `kasa/transports/sslcontext.py` with one shared SSL context for
the https transports to avoid copies across transports.
- Use it in `SslTransport`, and convert KLAP and Linkie also to use it.
- Extend Python's default ciphers with the legacy suites instead of
replacing accepted ciphers for future compatibility.

kasa/transports/ssltransport.py

@@ -31,6 +31,7 @@ from kasa.httpclient import HttpClient
 from kasa.json import dumps as json_dumps
 from kasa.json import loads as json_loads
 from kasa.transports import BaseTransport
+from kasa.transports.sslcontext import get_ssl_context
 
 _LOGGER = logging.getLogger(__name__)
 
@@ -151,6 +152,7 @@ class SslTransport(BaseTransport):
             url,
             json=request,
             headers=self.COMMON_HEADERS,
+            ssl=await get_ssl_context(),
         )
 
         if status_code != 200: