fix(proxy): handle ssl.SSLWantWriteError for large SSL responses

ssl.SSLSocket.send() raises ssl.SSLWantWriteError (not BlockingIOError)
when the underlying TCP buffer is full on a non-blocking SSL socket.
SSLWantWriteError is a subclass of OSError, so it was caught by the
generic connection-close handler, closing the connection mid-response.
The client socket stayed open, leaving the caller hanging indefinitely.

Catch SSLWantWriteError alongside BlockingIOError in both send paths so
SSL connections correctly register EVENT_WRITE and retry when buffer
space becomes available.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: nik-localstack

postgresql_proxy/proxy.py

@@ -267,7 +267,7 @@ def service_connection(self, key: SelectorKeyProxy, mask):
                 # All data drained; stop watching for writability.
                 conn.events = selectors.EVENT_READ
                 self.selector.modify(sock, selectors.EVENT_READ, data=conn)
-            except BlockingIOError:
+            except (BlockingIOError, ssl.SSLWantWriteError):
                 pass  # Still full; will retry on the next EVENT_WRITE notification.
             except OSError as e:
                 LOG.debug('%s closed while flushing backlog: %s', conn.name, e)
@@ -286,7 +286,7 @@ def service_connection(self, key: SelectorKeyProxy, mask):
                 if next_conn.events & selectors.EVENT_WRITE:
                     next_conn.events = selectors.EVENT_READ
                     self.selector.modify(next_conn.sock, selectors.EVENT_READ, data=next_conn)
-            except BlockingIOError:
+            except (BlockingIOError, ssl.SSLWantWriteError):
                 # next_conn's send buffer is full — register for writability so we retry when there's space.
                 if not (next_conn.events & selectors.EVENT_WRITE):
                     next_conn.events = selectors.EVENT_READ | selectors.EVENT_WRITE