Ensure types crates don't use alloc with CI

[nick-mobilecoin]

Update the crates to build with the thumbv7m-none-eabi target using
only the core crate from std

[nick-mobilecoin]

Current dependencies on/for this PR:

• main
  • PR Ensure types crates don't use alloc with CI #179 👈
    • PR Add Android and iOS for CI builds #181

This comment was auto-generated by Graphite.

[codecov-commenter]

Codecov Report

Merging #179 (0f7228c) into main (21b6ca2) will decrease coverage by 0.49%.
The diff coverage is 6.25%.

❗ Current head 0f7228c differs from pull request most recent head 5dfbed4. Consider uploading reports for the commit 5dfbed4 to get more accurate results

@@            Coverage Diff             @@
##             main     #179      +/-   ##
==========================================
- Coverage   88.08%   87.59%   -0.50%     
==========================================
  Files          41       41              
  Lines        2653     2668      +15     
==========================================
  Hits         2337     2337              
- Misses        316      331      +15     

Impacted Files	Coverage Δ
core/build/src/lib.rs	0.58% <0.00%> (-0.06%)	⬇️
core/types/src/lib.rs	100.00% <ø> (ø)
urts/sys/types/src/lib.rs	100.00% <ø> (ø)
core/types/src/error.rs	54.54% <100.00%> (ø)

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[awygle]

I think this is basically fine. It would be nice to have a more elegant solution but that doesn't seem to be possible given the current state of tooling.

[jcape]

LGTM, but I'd like to think about a few things: