fix(pg): do not treat Sync as connection ending

[devtechedge]

Summary

Fixes #3769.

Connection.sync() was setting _ending = true on every extended-query Sync. That flag exists so reportStreamError can ignore ECONNRESET / EPIPE during disconnect. Sync is the protocol barrier after Parse/Bind/Execute, not a disconnect, so after the first parameterized query those socket errors were silently dropped for the rest of the connection lifetime.

With pipeline: true that interacts badly with unexpected pooler/socket teardowns: the normal error path is closed and recovery depends only on the async close/end path, which can leave an in-flight query promise unsettled.

Changes

• Stop setting _ending in sync(); leave it set only in end() (Terminate) and the connect-timeout teardown path that already sets con._ending = true before destroying the stream.
• Add unit coverage that Sync leaves _ending false and that ECONNRESET after Sync still emits error (existing disconnect coverage still uses end()).

Test plan

• node test/unit/connection/error-tests.js (new cases green)
• Full packages/pg unit suite (find test/unit -name '*-tests.js' | xargs -n1 node) - 284 pass