Add subtick support

[dr3murr]

Related Issue

N/A

Implementation

Add subtick support (like CS:2) by sending the interpolation amount in the UserCmd (lerp_pos) whenever an attack occurs between ticks.

Screenshots

N/A

Checklist

• No other PRs implement this idea.
• This PR does not introduce any regressions.
• I certify that this PR is my own entirely original work, or I have permission from and have attributed the relevant authors.
• I have agreed to and signed this project's Contributor License Agreement.
• This PR targets the tc2-mod branch.

• This change has been filed as an issue.
• No other PRs address this.
• This PR is as minimal as possible.
• This PR does not introduce any regressions.
• This PR has been built and locally tested on at least one platform.
• This PR has been tested on all platforms, on both a dedicated server and on a listen server.

Testing Checklist

	Client	Server	Version
Windows	Tested	Tested	Windows 10
Linux	N/A	N/A

Caveats

Code probably needs to be cleaned up a lot
Probably breaks demo compatibility
In theory might break bots but I didn't notice any difference

Alternatives

Porting the game to Source 2 (DMCA)