fix: pin cbindgen to 0.29.0

[zachschuermann]

What changes are proposed in this pull request?

seems cbindgen is broken in 0.29.1? opened an issue over on their repo (see error i commented over there):

• cbindgen 0.29.1 failing to compile? mozilla/cbindgen#1114

in the meantime, pinning to 0.29.0 to unblock us.

How was this change tested?

cargo c before/after

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 84.65%. Comparing base (40bc46b) to head (c46b6f5).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1412   +/-   ##
=======================================
  Coverage   84.65%   84.65%           
=======================================
  Files         115      115           
  Lines       29601    29601           
  Branches    29601    29601           
=======================================
  Hits        25059    25059           
  Misses       3331     3331           
  Partials     1211     1211           

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