Move the to_chars and from_chars overloads into the boost::charconv namespace

[mborland]

Closes: #76

[cppalliance-bot]

An automated preview of the documentation is available at https://77.safe-numbers.prtest3.cppalliance.org/libs/safe_numbers/doc/html/index.html

If more commits are pushed to the pull request, the docs will rebuild at the same URL.

2026-02-18 15:39:14 UTC

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.6%. Comparing base (f5d7dc6) to head (7631d34).
⚠️ Report is 6 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff           @@
##           develop     #77   +/-   ##
=======================================
  Coverage     98.6%   98.6%           
=======================================
  Files          110     110           
  Lines         7099    7099           
  Branches      2429    2429           
=======================================
  Hits          6995    6995           
  Misses          43      43           
  Partials        61      61           

Files with missing lines	Coverage Δ
examples/charconv.cpp	100.0% <ø> (ø)
examples/verified_runtime_usage.cpp	92.7% <100.0%> (ø)
include/boost/safe_numbers/charconv.hpp	100.0% <ø> (ø)
test/test_unsigned_bounded_charconv.cpp	100.0% <ø> (ø)
test/test_unsigned_charconv.cpp	100.0% <ø> (ø)
test/test_verified_charconv.cpp	100.0% <100.0%> (ø)

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