Add palladium alloys

[natethegreatINL]

I added a new class of material, Palladium alloys. Of that class, I added two materials, Pd-Cu and Pd-Ag. I also added one new property to normal Palladium. This branch passed all the tests.

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.01% 🎉

Comparison is base (6464902) 98.70% compared to head (46f1c82) 98.72%.
Report is 2 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #264      +/-   ##
==========================================
+ Coverage   98.70%   98.72%   +0.01%     
==========================================
  Files          75       76       +1     
  Lines        1781     1800      +19     
==========================================
+ Hits         1758     1777      +19     
  Misses         23       23              

Files Changed	Coverage Δ
h_transport_materials/material.py	98.16% <100.00%> (+0.05%)	⬆️
..._transport_materials/property_database/__init__.py	100.00% <100.00%> (ø)
...transport_materials/property_database/palladium.py	100.00% <100.00%> (ø)
...rt_materials/property_database/palladium_copper.py	100.00% <100.00%> (ø)
...terials/property_database/pdag/palladium_silver.py	100.00% <100.00%> (ø)

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[RemDelaporteMathurin]

Hi @natethegreatINL thanks for this contribution!

We already have some PdAg data in HTM.
Does this overlap with these entries? If not, maybe we could use the new PalladiumAlloy class for those as well.

I'll have a look at the properties.

[RemDelaporteMathurin]

A few comments

[RemDelaporteMathurin]

some more comments about Piper's property