Fix lag application for negative lags

[tsalo]

Closes #35.

This PR corrects the calculation of negative lags.

Proposed Changes

• Remove unused lags parameter in rv function.
• Use the absolute lag when applying negative lags.
• Replace uses of numpy.int (deprecated) with int.

Change Type

• bugfix (+0.0.1)
• minor (+0.1.0)
• major (+1.0.0)
• refactoring (no version update)
• test (no version update)
• infrastructure (no version update)
• documentation (no version update)
• other

Checklist before review

• I added everything I wanted to add to this PR.
• [Code or tests only] I wrote/updated the necessary docstrings.
• [Code or tests only] I ran and passed tests locally.
• [Documentation only] I built the docs locally.
• My contribution is harmonious with the rest of the code: I'm not introducing repetitions.
• My code respects the adopted style, especially linting conventions.
• The title of this PR is explanatory on its own, enough to be understood as part of a changelog.
• I added or indicated the right labels.

• I added information regarding the timeline of completion for this PR.

• Please, comment on my PR while it's a draft and give me feedback on the development!

[smoia]

LGTM!

[smoia]

Actually, @tsalo, it's difficult for me to figure out which changes you wanted to stay - can you resolve the conflicts with master, please?

[tsalo]

Sorry for the delay @smoia. I'll give that a try now.

[tsalo]

I ended up having to change a few things. Lags were removed from rv at some point, but the parameter was still there, so I removed the parameter.

Also, lags in apply_lags wasn't applying lags correctly, AFAICT. I think I've fixed that.

[codecov]

Codecov Report

Merging #36 (f7c85b1) into master (24515ca) will not change coverage.
The diff coverage is 33.33%.

Additional details and impacted files

@@           Coverage Diff           @@
##           master      #36   +/-   ##
=======================================
  Coverage   47.04%   47.04%           
=======================================
  Files           7        7           
  Lines         321      321           
=======================================
  Hits          151      151           
  Misses        170      170           

Impacted Files	Coverage Δ
phys2denoise/metrics/cardiac.py	94.73% <ø> (ø)
phys2denoise/metrics/utils.py	69.56% <0.00%> (ø)
phys2denoise/metrics/chest_belt.py	85.54% <100.00%> (ø)