fix(tools): correct potentially unbound return for line_and_column

[Nytelife26]

This relates to...

The line_and_columns function of proselint/tools.py.

Rationale

The return type of this function is currently potentially unbound. As a result
of this, Python and various ecosystem tools are unable to determine its return
type accurately, even though we know it will never return an unbound.

Changes

• perf: prefer incrementation to enumeration
• fix(tools): correct return type for line_and_columns

Features

N/A.

Bug Fixes

N/A.

Breaking Changes and Deprecations

N/A.

[codecov]

Codecov Report

Merging #1181 (d6eb838) into main (f8e615e) will decrease coverage by 0.05%.
The diff coverage is 66.66%.

@@            Coverage Diff             @@
##             main    #1181      +/-   ##
==========================================
- Coverage   90.19%   90.13%   -0.06%     
==========================================
  Files          83       83              
  Lines        1203     1206       +3     
==========================================
+ Hits         1085     1087       +2     
- Misses        118      119       +1     

Flag	Coverage Δ
macos-latest	90.13% <66.66%> (-0.06%)	⬇️
py3.6	89.16% <66.66%> (-0.07%)	⬇️
py3.7	89.16% <66.66%> (-0.07%)	⬇️
py3.8	90.13% <66.66%> (-0.06%)	⬇️
py3.9	90.13% <66.66%> (-0.06%)	⬇️
pypypy3	89.16% <66.66%> (-0.07%)	⬇️
ubuntu-latest	90.13% <66.66%> (-0.06%)	⬇️
windows-latest	90.13% <66.66%> (-0.06%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
proselint/tools.py	77.44% <66.66%> (-0.13%)	⬇️

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