Prevent empty Round passes and type guarding

[jatkinson1000]

Closes #57

• Added a check to raise ValueError if empty iterable is passed to Round constructor.
• Also added some guards against archeryutils types passed to constructors.

Checklist:

• Source code updated to address issue
• Style and formatting applied
• Tests written to cover changes
• Docstrings included/updated in code
• Project documentation updated as necessary

[TomHall2020]

Seems fair, simple fixes.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.64%. Comparing base (fd2f524) to head (3c47ff1).

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #84      +/-   ##
==========================================
+ Coverage   97.61%   97.64%   +0.02%     
==========================================
  Files          28       28              
  Lines        1592     1611      +19     
==========================================
+ Hits         1554     1573      +19     
  Misses         38       38              

Files	Coverage Δ
archeryutils/rounds.py	100.00% <100.00%> (ø)
archeryutils/tests/test_rounds.py	100.00% <100.00%> (ø)