Reduce cyclomatic complexity in handler.match() and 100% test coverage for handlers.go

[steindvart]

Problem

• Closes #221

Solution - what PR does

• Comprehensive decomposition of the function (h handler) match(update *models.Update). To reduce cyclomatic complexity, and improve testability.

Now, for handlers.go file, the following indicators apply:

$ gocyclo handlers.go
9 bot getDataFromUpdate handlers.go:72:1
9 bot (handler).match handlers.go:44:1
5 bot (handler).matchCommandStartOnly handlers.go:137:1
4 bot (handler).matchCommand handlers.go:125:1
4 bot extractCommand handlers.go:116:1
3 bot (*Bot).UnregisterHandler handlers.go:205:1
1 bot (*Bot).RegisterHandler handlers.go:186:1
1 bot (*Bot).RegisterHandlerRegexp handlers.go:167:1
1 bot (*Bot).RegisterHandlerMatchFunc handlers.go:149:1
1 bot (handler).matchRegexp handlers.go:112:1
1 bot (handler).matchContains handlers.go:108:1
1 bot (handler).matchPrefix handlers.go:104:1
1 bot (handler).matchExact handlers.go:100:1

Previous:

$ gocyclo handlers.go                                                                                                                                                               
23 bot (handler).match handlers.go:43:1
3 bot (*Bot).UnregisterHandler handlers.go:165:1
1 bot (*Bot).RegisterHandler handlers.go:146:1
1 bot (*Bot).RegisterHandlerRegexp handlers.go:127:1
1 bot (*Bot).RegisterHandlerMatchFunc handlers.go:109:1

• Achieving 100% branch coverage for the all added code.
• Achieving 100% test coverage for the handlers.go file.

[codecov-commenter]

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Codecov Report

:white_check_mark: All modified and coverable lines are covered by tests. :white_check_mark: Project coverage is 47.85%. Comparing base (1efca4f) to head (ddec830). :warning: Report is 1 commits behind head on main. :exclamation: Your organization needs to install the Codecov GitHub app to enable full functionality.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #222      +/-   ##
==========================================
+ Coverage   45.30%   47.85%   +2.54%     
==========================================
  Files          29       29              
  Lines        2355     2123     -232     
==========================================
- Hits         1067     1016      -51     
+ Misses       1241     1063     -178     
+ Partials       47       44       -3     

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