refactor and deprecate old equiformerv2

[misko]

Moving forward equiformer v2 should be invoked through hydra using both a head and backbone. This moves the original code (required to load from a checkpoint) to a deprecated status.

[codecov]

Codecov Report

Attention: Patch coverage is 88.16327% with 29 lines in your changes missing coverage. Please review.

Files	Patch %	Lines
...e/models/equiformer_v2/equiformer_v2_deprecated.py	91.15%	20 Missing ⚠️
...airchem/core/models/equiformer_v2/equiformer_v2.py	50.00%	9 Missing ⚠️

Files	Coverage Δ
src/fairchem/core/models/equiformer_v2/__init__.py	100.00% <100.00%> (ø)
...airchem/core/models/equiformer_v2/equiformer_v2.py	80.91% <50.00%> (-8.02%)	⬇️
...e/models/equiformer_v2/equiformer_v2_deprecated.py	91.15% <91.15%> (ø)

[rayg1234]

Thanks for doing this! minor ask: can you also separate the tests to test_equiformers_v2_deprecated and test_equiformers_v2 (https://github.com/FAIR-Chem/fairchem/blob/main/tests/core/models/test_equiformer_v2.py) this way someone can just delete the *deprecated.py without accidentally deleting the activation checkpointing test or new tests on the backbone/hydra only for example