fix: to_str not available on all abi3 builds

[davidhewitt]

fixes #59

[codecov]

Codecov Report

Attention: Patch coverage is 14.28571% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 80.41%. Comparing base (5c456a8) to head (c3a4587).

Files	Patch %	Lines
src/de.rs	16.66%	1 Missing and 4 partials ⚠️
src/ser.rs	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #60   +/-   ##
=======================================
  Coverage   80.41%   80.41%           
=======================================
  Files           3        3           
  Lines        1062     1062           
  Branches     1062     1062           
=======================================
  Hits          854      854           
  Misses        160      160           
  Partials       48       48           

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.