Thunk lock handling

[raviqqe]

Close #648.

As described in #648, we might want to implement some other methods like blackholing eventually in the future. But we implement the most naive method of yielding from green threads cooperatively for simplicity in this PR.

[codecov-commenter]

Codecov Report

Merging #774 (e91e2e1) into main (753a3c4) will increase coverage by 0.01%.
The diff coverage is 97.77%.

@@            Coverage Diff             @@
##             main     #774      +/-   ##
==========================================
+ Coverage   85.31%   85.33%   +0.01%     
==========================================
  Files         311      312       +1     
  Lines       29015    29040      +25     
==========================================
+ Hits        24755    24780      +25     
  Misses       4260     4260              

Impacted Files	Coverage Δ
lib/mir-fmm/src/entry_functions.rs	97.40% <96.96%> (+0.09%)	⬆️
lib/mir-fmm/src/lib.rs	100.00% <100.00%> (ø)
lib/mir-fmm/src/yield_.rs	100.00% <100.00%> (ø)

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