feat: Allow overriding the coroutine runner in start_server()

[achimnol]

In Python 3.16, event loop policies will be depreacted.

Let's allow setting the runner function as an optional kwarg in aiotools.start_server() so that our users could use it to set as uvloop.run for forward compatibility.

[codecov]

Codecov Report

❌ Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 80.15%. Comparing base (11c8347) to head (c091099).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/aiotools/server.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #99      +/-   ##
==========================================
+ Coverage   79.94%   80.15%   +0.20%     
==========================================
  Files          21       21              
  Lines        1456     1456              
==========================================
+ Hits         1164     1167       +3     
+ Misses        292      289       -3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.