feat: add ReplicateConVar

[21Joakim]

This PR is based on #563 but I have removed the client checks (as they are not necessary) which makes this easier to maintain.

I have tested and validated that everything works correctly on Linux, the core ReplicateConVar code is also identical to the implementation in CS2Fixes (https://github.com/Source2ZE/CS2Fixes/blob/e9dfd9a08b7158c313221019d34e8586a6396d5a/src/playermanager.cpp#L567-L580) and uses all the same features which UserMessage already relies on, no additional signatures or offsets.

I have tested this with sv_autobunnyhopping and sv_enablebunnyhopping using the plugin below to enable bhop on a per player basis and I have not encountered any issues, I tested this with a friend to ensure it was properly setting per player.

Here is a simple bhop example plugin https://gist.github.com/21Joakim/480f2bae588df54d2f34faba8b2861bc, simply use the bhop console command to toggle bhop on and off for your player only.

I did some additional tests to ensure it is safe to use

• ✅ Passing a convar which is not replicated does not cause any issues
• ✅ Passing an invalid convarname (i.e. a convar which does not exist) does not cause any issues
• ✅ Passing an invalid convarvalue (e.g. a string for a bool value) for the provided convarname convar does not cause any issues
• ✅ Replicating the convar for a bot does not cause any issues
• ✅ Passing an invalid slot (i.e. a negative slot or a slot which does not have a player) does not cause any issues
• ✅ Passing an empty value for either (or both) of convarname or convarvalue does not cause any issues
• ✅ Creating a UserMessage hook for SetConvar works as expected, it sees the messages emitted by ReplicateConVar and there are no issues with sending the UserMessage from within the hook
• ❌ Passing a null value for convarname or convarvalue will cause a segfault, this happens for other native functions as well (e.g. player.ExecuteClientCommand(null)) so probably more of a systemic problem if anything

I have been waiting for the original PR to be merged for almost 5 months so I am hoping that by cutting the feature down to the core and testing it thoroughly we can have this new PR merged quickly!

[KillStr3aK]

LGTM