Add ability to specify server port from cli

[just-an-engineer]

It now looks to see if a port number was specified on the command line, and tries to use that before looking at the config file or environment variables
Since --start-server calls InternalStartServer under the hood, I have it starting it with the port number specified as the environment variable, although I can change it to also take it from the cli.
Added tests and updated the readme for usages

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 32.82443% with 88 lines in your changes missing coverage. Please review.

Project coverage is 51.79%. Comparing base (0cc0c62) to head (f07dc9b).
Report is 72 commits behind head on main.

Files with missing lines	Patch %	Lines
src/util.rs	27.27%	13 Missing and 43 partials ⚠️
src/commands.rs	36.36%	2 Missing and 12 partials ⚠️
src/config.rs	43.75%	1 Missing and 8 partials ⚠️
src/cmdline.rs	42.85%	0 Missing and 8 partials ⚠️
tests/oauth.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #2239       +/-   ##
===========================================
+ Coverage   30.91%   51.79%   +20.87%     
===========================================
  Files          53       54        +1     
  Lines       20112    20550      +438     
  Branches     9755     9540      -215     
===========================================
+ Hits         6217    10643     +4426     
- Misses       7922     7956       +34     
+ Partials     5973     1951     -4022     

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[sylvestre]

What about configuring it in a configuration file?

[just-an-engineer]

Yeah, I can do that. I'll add that as well

[just-an-engineer]

Alright, just added that in. Currently, this is the order of precedence in the code of where it looks for the port: CLI, config, env var, and lastly, the hardcoded default port of 4226. No particular reason for that order, so that can be changed up if desired.

[just-an-engineer]

@sylvestre, I'm a bit new to the whole process. At this point, do I select "Update branch"? Do I want for someone else to do something?

[just-an-engineer]

I realized I hadn't done anything for commands outside of start or stop. So I added in basic functionality for a client cache (which we can expand to other things), and added tests for that. I also corrected a prior test that was incorrect, I just wasn't thinking properly for that one. I also expanded it to test that a compile request works for a server started on a non-default port.
The client cache will also help it be more ergonomic for users because they won't have to specify an environment variable alongside every sccache command they run, because if they started a server on a different port, they'd have to use the env vars to see its stats, run a compile request, etc. This can make it a bit more streamlined by assuming that you'll have a single compile server you primarily use (if that's not the case, this may break down, but it's not like it was easier beforehand), and once you specify it, that's the one you want to see the stats for, run compile jobs from, and shutdown