feat: Add bfloat16 support

[aturker-synnada]

Description

Closes #133.

What is Changed

Include the changes introduced in this PR.

• Backends now supports bfloat16.

Checklist:

• Tests that cover the code added.
• Corresponding changes documented.
• All tests passed.
• The code linted and styled (pre-commit run --all-files has passed).

[codecov]

Codecov Report

Attention: Patch coverage is 96.93878% with 3 lines in your changes missing coverage. Please review.

Project coverage is 88.85%. Comparing base (d65d013) to head (f214de0).

Files with missing lines	Patch %	Lines
mithril/backends/backend.py	83.33%	1 Missing ⚠️
...hril/backends/with_autograd/jax_backend/backend.py	92.30%	1 Missing ⚠️
...hril/backends/with_autograd/mlx_backend/backend.py	91.66%	1 Missing ⚠️

@@            Coverage Diff             @@
##             main     #136      +/-   ##
==========================================
+ Coverage   88.81%   88.85%   +0.03%     
==========================================
  Files          61       61              
  Lines       15421    15474      +53     
==========================================
+ Hits        13696    13749      +53     
  Misses       1725     1725              

Files with missing lines	Coverage Δ
mithril/__init__.py	77.77% <ø> (ø)
mithril/backends/utils.py	90.90% <100.00%> (+15.90%)	⬆️
...ithril/backends/with_autograd/jax_backend/utils.py	71.02% <100.00%> (+0.50%)	⬆️
...ithril/backends/with_autograd/mlx_backend/utils.py	61.49% <100.00%> (+0.73%)	⬆️
...il/backends/with_autograd/torch_backend/backend.py	92.55% <100.00%> (+0.13%)	⬆️
...hril/backends/with_autograd/torch_backend/utils.py	81.34% <100.00%> (+0.16%)	⬆️
.../backends/with_manualgrad/numpy_backend/backend.py	88.77% <100.00%> (+0.12%)	⬆️
...il/backends/with_manualgrad/numpy_backend/utils.py	74.85% <100.00%> (+0.44%)	⬆️
mithril/core.py	86.95% <100.00%> (+0.59%)	⬆️
mithril/backends/backend.py	63.95% <83.33%> (ø)
... and 2 more