Fix edge_rot_mat

[misko]

We currently rotate edges to align with the y-axis, leaving one degree of freedom (rotation about this axis).
The ensure equivariance we randomly sample a direction along this degree of freedom. However in the current implementation it is not a uniform circular distribution, but instead biased by edges of a cube.
This corrects the issue and also speeds up the computation.

[codecov]

Codecov Report

Attention: Patch coverage is 97.05882% with 1 line in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/fairchem/core/models/escn/edge_rot_mat.py	96.29%	1 Missing ⚠️

Files with missing lines	Coverage Δ
...airchem/core/models/equiformer_v2/equiformer_v2.py	80.40% <100.00%> (-0.16%)	⬇️
...e/models/equiformer_v2/equiformer_v2_deprecated.py	91.07% <100.00%> (-0.08%)	⬇️
src/fairchem/core/models/escn/escn.py	96.05% <100.00%> (+0.40%)	⬆️
src/fairchem/core/models/escn/edge_rot_mat.py	96.29% <96.29%> (ø)

... and 1 file with indirect coverage changes