Scope

• Treat non-I/O TLS errors as non-backpressure errors.
• Test a non-I/O TLS error does not result in backpressure error handling (clears pool and marks server unknown)

Background & Motivation
Quoting CMAP spec:

For errors that the driver can distinguish as never occurring due to server overload, such as DNS lookup failures, non‑I/O TLS errors (e.g., certificate validation or hostname‑mismatch failures), or errors encountered while establishing a connection to a SOCKS5 proxy, the driver MUST NOT add backpressure error labels for these error types

The C driver does not have an existing way to distinguish between non-I/O TLS errors.

See comment for implementation suggestions.

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