Feature 107 cancel scans from paused state

[epi052]

closes #107

Landing a Pull Request (PR)

Long form explanations of most of the items below can be found in the CONTRIBUTING guide.

Branching checklist

• There is an issue associated with your PR (bug, feature, etc.. if not, create one)
• Your PR description references the associated issue (i.e. fixes [FEATURE REQUEST] Dynamically tuning concurrency/connection limit or bailing after n connection failures #123)
• Code is in its own branch
• Branch name is related to the PR contents
• PR targets master

Static analysis checks

• All rust files are formatted using cargo fmt
• All clippy checks pass when running cargo clippy --all-targets --all-features -- -D warnings -A clippy::unnecessary_unwrap
• All existing tests pass

Documentation

• New code is documented using doc comments
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Additional Tests

• New code is unit tested
• New code is integration tested, as needed
• New tests pass

[codecov]

Codecov Report

Merging #121 (3881789) into master (b48445f) will decrease coverage by 0.85%.
The diff coverage is 87.07%.

@@            Coverage Diff             @@
##           master     #121      +/-   ##
==========================================
- Coverage   94.64%   93.79%   -0.86%     
==========================================
  Files          12       13       +1     
  Lines        2036     2208     +172     
==========================================
+ Hits         1927     2071     +144     
- Misses        109      137      +28     

Impacted Files	Coverage Δ
src/main.rs	90.74% <ø> (ø)
src/scanner.rs	92.06% <70.00%> (-1.26%)	⬇️
src/scan_manager.rs	88.47% <88.47%> (ø)

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