Apply RAII to `UnixSocket`

[JosiahWI]

This deletes the UnixSocket copy constructors and adds move constructors and a destructor. The NetAccept and NetAcceptEvent classes now store shared pointers to their server instances because of this change.

Todo:

• [ ] Implement a way to release the file descriptor from a UnixSocket, necessary because SSL takes ownership of it.
• [ ] Close the socket in the UnixSocket destructor if it is still valid.

[JosiahWI]

The last run of the AuTest remap_acl failed:

       Test : Checking that ReturnCode == 0 - Failed
          Reason: Returned Value 70 != 0
       file /tmp/sandbox/remap_acl/ts-140/log/diags.log : Diags log file diags.log should not contain errors - Passed
          Reason: Contents of /tmp/sandbox/remap_acl/ts-140/log/diags.log excludes expression
       file /tmp/sandbox/remap_acl/ts-140/log/diags.log : Diags log file diags.log should not contain errors - Failed
          Reason: Contents of /tmp/sandbox/remap_acl/ts-140/log/diags.log contains expression: "FATAL:"
             Details:
               [Oct 14 12:24:49.592] traffic_server FATAL: Could not bind or listen to port 44683, mptcp enabled: 0 (error: 98) Address already in use -1 : 37
               ```

[github-actions[bot]]

This pull request has been automatically marked as stale because it has not had recent activity. Marking it stale to flag it for further consideration by the community.