support timeout when Dial

[tyws]

1. Are you opening this pull request for bug-fix, optimization or new feature?

new feature

2. Please describe how these code changes achieve your intention.

add new functions use net.DialTiemout to create connection

3. Please link to the relevant issues (if any).

4. What documentation changes (if any) need to be made/updated because of this PR?

4. Checklist

• I have squashed all insignificant commits.
• I have commented my code for explaining package types, values, functions, and non-obvious lines.
• I have written unit tests and verified that all tests passes (if needed).
• I have documented feature info on the README (only when this PR is adding a new feature).
• (optional) I am willing to help maintain this change if there are issues with it later.

[panjf2000]

Thank you for the PR! But I'm not sure we need this feature. If the users want to dial with a timeout, they can call net.DialTimeout to get the net.Conn and pass it to Client.Enroll.