fix: enforce socket deadlines during prelogin in encrypt=strict TLS mode

[dlevy-msft-sql]

Problem

In the encrypt=strict TLS path in tds.go, getTLSConn replaces outbuf.transport with a *tls.Conn, which bypasses the timeoutConn wrapper. This means the computed preloginTimeout (and even the original ConnTimeout) won't enforce a socket deadline in strict mode. Without a context deadline/cancel, readPrelogin can still hang indefinitely in this path.

Context

Identified during review of PR #360 (which fixed the non-strict prelogin hang). The strict mode path was out of scope for that change.

Suggested Fix

Ensure the TLS strict mode wraps the timeout-aware conn, e.g. pass the timeoutConn itself into tls.Client or otherwise apply read/write deadlines on the underlying net.Conn during prelogin.