Refactor for speed and consistency

[Flamefire]

1. Consistently pass string_view by value as is best practice with it being a pointer-size pair
2. Move try_to_int to new header moving it out of a header containing the large base_num_format.
3. Use Boost.Charconv in try_to_int
4. Allow try_to_int to be used with other integer types, e.g. the unsigned as used with in one other place
5. Avoid superflous copies of the time zone string: First into a local variable, then into a vector to have it non-const. The latter is only required for FreeBSD and apple, not for all Linux systems.
6. Test only: Return the success state in TEST macro to allow depending on the return value for further tests

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.87%. Comparing base (5a58e65) to head (e540a63).
Report is 11 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop     #252   +/-   ##
========================================
  Coverage    95.87%   95.87%           
========================================
  Files          117      119    +2     
  Lines        10406    10410    +4     
========================================
+ Hits          9977     9981    +4     
  Misses         429      429           

Files with missing lines	Coverage Δ
include/boost/locale/boundary/boundary_point.hpp	100.00% <ø> (ø)
include/boost/locale/boundary/index.hpp	98.77% <ø> (ø)
include/boost/locale/boundary/segment.hpp	100.00% <ø> (ø)
include/boost/locale/detail/any_string.hpp	100.00% <100.00%> (ø)
include/boost/locale/detail/encoding.hpp	100.00% <100.00%> (ø)
include/boost/locale/encoding.hpp	100.00% <100.00%> (ø)
include/boost/locale/format.hpp	97.82% <ø> (ø)
include/boost/locale/formatting.hpp	100.00% <ø> (ø)
include/boost/locale/message.hpp	100.00% <ø> (ø)
src/encoding/codepage.cpp	100.00% <ø> (ø)
... and 26 more

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5a58e65...e540a63. Read the comment docs.