client-only permessage-deflate still sends server headers

I'm using boost 1.81 and beast to connect as a client to a remote websocket host, and with compression disabled, everything works fine.

This endpoint supports permessage-deflate from clients, and will also fail to upgrade if any server deflate headers are included.

If I try to add compression like so:
```
auto ret = std::make_shared(io_ctx, ssl_ctx);
boost::beast::websocket::permessage_deflate pd_option{false, true};
ret->set_option(pd_option);
```

The upgrade headers still include `server_max_window_bits`, and the websocket upgrade is rejected. The issue seems to be in the translation between `pd_option` and beast's internal `pmd_offer`; the latter seems to support client and server at once only.

Attempts to set the server window size to 0 to prevent the field from being written (looking at the source of pmd_extension.ipp) yield an invalid value error.

Would it be possible for `pmd_offer` to respect the `pd_option`'s server_enable flag and not send those headers?