GODRIVER-2218 Bump connection idle deadline on pool checkIn.

[matthewdale]

GODRIVER-2218

Currently a connection's "idle deadline" is increased in the Go driver only when reading writing to the connection. However, the CMAP spec defines "idle" as:

Idle: The Connection is currently "available" (as defined below) and has been for longer than maxIdleTimeMS.

"Available" is defined as:

The Connection has been established and is waiting in the pool to be checked out.

As a result, it's currently possible to check in a connection to the pool that has not been read from or written to for more than maxIdleTimeMS and it will be considered stale due to idle timeout. According to the definition of "idle" in the CMAP spec, that should be impossible.

Bump the connection idle deadline when checking connections into the pool.

Changes:

• Run conn.bumpIdleDeadline() in pool.checkInNoEvent().
• Remove all other calls to conn.bumpIdleDeadline() because they are now unnecessary.
• Add a test that asserts checked-out but unused connections are not considered idle.
• Add a test that asserts connections checked in by maintain() have an idle deadline set.

[benjirewis]

I think those failures on latest are unrelated?

[kevinAlbs]

LGTM. Good catch on the mismatched behavior with the spec!