fix(ts): Add defensive guards on geometry decode paths

[CommanderStorm]

Split out from #1462

Adds named-error guards on the geometry decode paths.
Missing vertex/triangle/offset buffers/ morton settings fail with a clear message instead of a later errors.

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[codecov-commenter]

Codecov Report

❌ Patch coverage is 97.43590% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 96.14%. Comparing base (5c0ae60) to head (a508ab5).
⚠️ Report is 86 commits behind head on main.

Files with missing lines	Patch %	Lines
ts/src/decoding/geometryDecoder.ts	90.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1470       +/-   ##
===========================================
+ Coverage   63.96%   96.14%   +32.18%     
===========================================
  Files          88       68       -20     
  Lines       14440     4935     -9505     
  Branches        0      779      +779     
===========================================
- Hits         9236     4745     -4491     
+ Misses       5204      175     -5029     
- Partials        0       15       +15     

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[HarelM]

Are these possible code flows? I'm not very keen on defensive programing...

[HarelM]

Looking at the errors that were added, I'm not sure they are a lot better than "x is not a property of undefined", as they don't really help understanding where the issue actually is and how to solve it.
IDK...

[CommanderStorm]

The issues should not be producible on valid input by definition.
So if we design our encoders well, they are impossible by construction.

Problem is that I still will have undefined in the type, and that is not something I think I can fix..

[CommanderStorm]

If we want ts6, strict mode seems to be one of the requirements, so therefore we need to actually handle our undefined..