Makes ion-hash a feature of ion-rs

[popematt]

Issue #, if available:

Resolves #454

Description of changes:

• Moves ion-hash from its own crate into ion-rs
• Moves the ion-hash-tests submodule to the root of the repo
• Updates the GHA workflow to run cargo tests with no features and with all features.
• Creates a new version of ion-hash crate to essentially tombstone the package.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov]

Codecov Report

Patch coverage: 80.00% and no project coverage change.

Comparison is base (f49659e) 90.14% compared to head (dda6d3f) 90.14%.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #478   +/-   ##
=======================================
  Coverage   90.14%   90.14%           
=======================================
  Files          76       77    +1     
  Lines       13568    13568           
=======================================
  Hits        12231    12231           
  Misses       1337     1337           

Impacted Files	Coverage Δ
ion-hash/src/lib.rs	100.00% <ø> (ø)
src/ion_hash/element_hasher.rs	98.00% <ø> (ø)
src/ion_hash/representation.rs	99.00% <ø> (ø)
src/ion_hash/type_qualifier.rs	100.00% <ø> (ø)
src/lib.rs	87.22% <ø> (ø)
tests/ion_hash_tests.rs	80.98% <50.00%> (ø)
src/ion_hash/mod.rs	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[zslayton]

yessss 🚀

One question about optional dependencies below. If it's straightforward, can you address the clippy warnings before merging? (With the exception of the redundant closure warning, which is caused by issue #472.)

[zslayton]

Does this mean that the optional digest dependency should be included when the ion-hash feature is enabled? If so, should sha2 also be in this list?

[popematt]

This means that ion-hash will automatically bring in digest. I don't think it should bring in sha2 because sha2 is not required. Someone might want to use md5 or another hash function instead.