exception handling in at_lookup's BaseConnection.write

[gkc]

Describe the bug

While looking at this code in the course of investigating another issue, I observed two problems
(1) exception is silently swallowed
(2) write() is not followed by flush()

Steps to reproduce

n/a

Expected behavior

• if we want to catch exceptions here rather than via the socket.done error handler, we should await socket.flush() after the call to socket.write()
• we should rethrow exceptions if they occur

Being part of the core client-side network comms code, changes here have a large blast radius if they introduce a new problem so while the impl here is straightforward, the testing will need to be comprehensive

Screenshots

No response

Smartphones

No response

Were you using an atApplication when the bug was found?

No response

Additional context

No response

[murali-shris]

Will be taken up in PR102