Handle signal stop and continue

[pvdrz]

Describe the changes done on this pull request
This PR allows sudo to properly handle stopping and continuing when receiving signals.

I think this is easier to review commit-per-commit.

This is the last chunk of #363 and it is blocked by #519.

Pull Request Checklist

• I have read and accepted the code of conduct for this project.
• I have tested, formatted and ran clippy over my changes.
• I have commented and documented my changes.
• This pull request will fix issues Sudo-rs hangs when you suspend a process with ^Z #245, sudo-rs ignores SIGTSTP signal #325 and sudo-rs does not set the terminal foreground process group #360 where a proper discussion about a solution has taken place.

[github-actions]

Number of dependencies and binary size impact report

Metric	main	PR #520	Delta
Direct dependencies	5	5	-
Total dependencies	10	10	-
Binary size	580.6 KiB	615.8 KiB	+6.1%
Text size	343.3 KiB	363.3 KiB	+5.8%

Dependencies diff

 └─ sudo-rs [v0.1.0-dev.20230620]
    ├─ glob [v0.3.1]
    ├─ libc [v0.2.146]
    ├─ log [v0.4.19]
    ├─ signal-hook [v0.3.15]
    |  ├─ libc [v0.2.146]
    |  ├─ signal-hook-registry [v1.4.1]
    |  |  └─ libc [v0.2.146]
    |  └─ cc [v1.0.79]
    └─ signal-hook-registry [v1.4.1]

[codecov]

Codecov Report

Patch coverage: 67.65% and project coverage change: -0.75 ⚠️

Comparison is base (ac84636) 86.35% compared to head (1d78111) 85.61%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #520      +/-   ##
==========================================
- Coverage   86.35%   85.61%   -0.75%     
==========================================
  Files          57       59       +2     
  Lines        7412     7834     +422     
==========================================
+ Hits         6401     6707     +306     
- Misses       1011     1127     +116     

Impacted Files	Coverage Δ
src/system/term/user_term.rs	62.34% <7.69%> (+62.34%)	⬆️
src/exec/use_pty/monitor.rs	53.30% <64.06%> (ø)
src/exec/mod.rs	75.64% <66.66%> (-17.91%)	⬇️
src/exec/no_pty.rs	67.40% <67.40%> (ø)
src/exec/use_pty/parent.rs	71.03% <75.26%> (ø)
src/exec/use_pty/pipe.rs	80.95% <80.95%> (ø)
src/exec/event.rs	84.31% <100.00%> (-3.99%)	⬇️
src/exec/use_pty/backchannel.rs	86.91% <100.00%> (ø)
src/system/wait.rs	87.85% <100.00%> (+0.35%)	⬆️

... and 4 files with indirect coverage changes

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