feat: Remove file type from thumbnail names

[gpeacock]

This is a c2pa 2.2 spec requirement
This now also adds support for the EmbeddedData Assertion - we should be using that for future thumbnail generation.

[codecov]

Codecov Report

❌ Patch coverage is 89.44954% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.83%. Comparing base (2ab141d) to head (dabf57c).
⚠️ Report is 31 commits behind head on main.

Files with missing lines	Patch %	Lines
sdk/src/assertion.rs	76.00%	6 Missing ⚠️
sdk/src/assertions/thumbnail.rs	81.48%	5 Missing ⚠️
sdk/src/builder.rs	50.00%	5 Missing ⚠️
sdk/src/ingredient.rs	81.81%	4 Missing ⚠️
sdk/src/assertions/embedded_data.rs	96.10%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1187      +/-   ##
==========================================
+ Coverage   79.57%   79.83%   +0.25%     
==========================================
  Files         147      148       +1     
  Lines       40551    43462    +2911     
==========================================
+ Hits        32268    34696    +2428     
- Misses       8283     8766     +483     

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[tmathern]

Sidenote - you will need a version of #1193 too. Whichever PR pickes it up first and merged first "wins" the right to have more passing checks again.

[ok-nick]

I'm assuming we already support the __1 naming requirement for v2 ingredient thumbnail labels too?