refactor: implement `get_header_as_int` method

[vgerak]

Summary of Changes

Implements the get_header_as_int method.

Wasn't sure whether (and how) to document it in the docs, as I couldn't find the part for the similar function get_header_as_datetime().

Related Issues

2060

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[codecov[bot]]

Codecov Report

Merging #2117 (6c94651) into master (44b1596) will not change coverage. The diff coverage is n/a.

:exclamation: Current head 6c94651 differs from pull request most recent head 8bd22bb. Consider uploading reports for the commit 8bd22bb to get more accurate results

@@            Coverage Diff            @@
##            master     #2117   +/-   ##
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  Coverage   100.00%   100.00%           
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  Files           55        55           
  Lines         5553      5552    -1     
  Branches       880       880           
=========================================
- Hits          5553      5552    -1     

Impacted Files	Coverage Δ
falcon/constants.py	100.00% <0.00%> (ø)

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[vgerak]

@vytas7 pinging issue creator

[vytas7]

Hi @vgerak! And thanks for this PR, and sorry I've been swamped with other things recently not directly related to Falcon in any way, so I couldn't review in a timely fashion. (If you want to count this towards Hacktoberfest, I've tentatively added the relevant label that should do the job.)

It seems that there are unrelated issues with our CI which must be addressed prior to proceeding with your PR, I'll try to prioritize this when I find some free time.