Keep boto3 optional

[munrojm]

This PR ensures boto3 remains an optional dependency.

[codecov-commenter]

Codecov Report

Patch coverage: 41.80% and project coverage change: -10.21% ⚠️

Comparison is base (3ffecd2) 79.85% compared to head (6fc721c) 69.64%.
Report is 26 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #836       +/-   ##
===========================================
- Coverage   79.85%   69.64%   -10.21%     
===========================================
  Files          38       51       +13     
  Lines        1881     2418      +537     
===========================================
+ Hits         1502     1684      +182     
- Misses        379      734      +355     

Files Changed	Coverage Δ
mp_api/client/routes/_user_settings.py	100.00% <ø> (ø)
mp_api/client/routes/materials/absorption.py	32.25% <ø> (ø)
mp_api/client/routes/materials/alloys.py	52.63% <ø> (ø)
mp_api/client/routes/materials/bonds.py	93.33% <ø> (ø)
mp_api/client/routes/materials/chemenv.py	85.10% <ø> (ø)
mp_api/client/routes/materials/dielectric.py	92.85% <ø> (ø)
mp_api/client/routes/materials/doi.py	100.00% <ø> (ø)
mp_api/client/routes/materials/elasticity.py	96.77% <ø> (ø)
mp_api/client/routes/materials/electrodes.py	91.30% <ø> (ø)
mp_api/client/routes/materials/eos.py	94.73% <ø> (ø)
... and 37 more

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