add further type hints.

[braniii]

Fixes comment 2 from openjournals/joss-reviews#10244 (comment)

@dieJaegerIn I've added the missing type hints. Feel free to merge if it looks good to you.

[codecov]

Codecov Report

❌ Patch coverage is 96.42857% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 89.37%. Comparing base (ca7fa02) to head (010d316).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/dcTMD/io.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #37      +/-   ##
==========================================
+ Coverage   89.29%   89.37%   +0.08%     
==========================================
  Files          11       11              
  Lines         607      612       +5     
==========================================
+ Hits          542      547       +5     
  Misses         65       65              

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

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.