More tests for hypercalls

[jounathaen]

• Test for removing files
• Test for lseek

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.65%. Comparing base (9448b19) to head (5d61fb9).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #893      +/-   ##
==========================================
+ Coverage   71.02%   71.65%   +0.62%     
==========================================
  Files          25       25              
  Lines        3179     3179              
==========================================
+ Hits         2258     2278      +20     
+ Misses        921      901      -20     

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[jounathaen]

Merging this without the lseek test, as lseek is currently not implemented in hermit (see hermit-os/hermit-rs#652)