Switch to pyrepl

[A5rocks]

This cleans up some code and makes Linux support work even on some systems configured without TIOCSTI. Fixes #3007, closes #3306.

I didn't try this out on Windows, and pyrepl simply cannot be tested easily in CI on Windows, so that may be broken. Please try this out!

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00000%. Comparing base (a97133a) to head (e876d78).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@               Coverage Diff               @@
##                 main        #3453   +/-   ##
===============================================
  Coverage   100.00000%   100.00000%           
===============================================
  Files             128          128           
  Lines           19417        19438   +21     
  Branches         1317         1307   -10     
===============================================
+ Hits            19417        19438   +21     

Files with missing lines	Coverage Δ
src/trio/_repl.py	100.00000% <100.00000%> (ø)
src/trio/_tests/test_repl.py	100.00000% <100.00000%> (ø)

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[A5rocks]

I took the opportunity to run the REPL input loop in the main thread too, since it seemed easy enough. One downside is that, since the version of pyrepl on PyPI has a bug w/r/t non-blocking operation, CPython w/ 3.12 or less will have a worse experience in the REPL.