refactor(x/data): remove oneof and update validation

[ryanchristo]

Description

Closes: #872

This pull request updates ContentHash to no longer use oneof, which breaks amino signing. This pull request also improves validation checks and updates MediaType to RawMediaType, which is specific to raw content hashes and aligns with the namespace used for graph content hashes.

---

Author Checklist

All items are required. Please add a note to the item if the item is not applicable and
please add links to any relevant follow up issues.

I have...

• included the correct type prefix in the PR title
• added ! to the type prefix if API or client breaking change
• targeted the correct branch (see PR Targeting)
• provided a link to the relevant issue or specification
• followed the guidelines for building modules
• included the necessary unit and integration tests
• added a changelog entry to CHANGELOG.md
• included comments for documenting Go code
• updated the relevant documentation or specification
• reviewed "Files changed" and left comments if necessary
• confirmed all CI checks have passed

Reviewers Checklist

All items are required. Please add a note if the item is not applicable and please add
your handle next to the items reviewed if you only reviewed selected items.

I have...

• confirmed the correct type prefix in the PR title
• confirmed ! in the type prefix if API or client breaking change
• confirmed all author checklist items have been addressed
• reviewed state machine logic
• reviewed API design and naming
• reviewed documentation is accurate
• reviewed tests and test coverage
• manually tested (if applicable)

[codecov]

Codecov Report

Merging #946 (77d7166) into master (70cba99) will increase coverage by 0.06%.
The diff coverage is 97.67%.

❗ Current head 77d7166 differs from pull request most recent head e478d12. Consider uploading reports for the commit e478d12 to get more accurate results

@@            Coverage Diff             @@
##           master     #946      +/-   ##
==========================================
+ Coverage   73.15%   73.21%   +0.06%     
==========================================
  Files         196      196              
  Lines       23155    23116      -39     
==========================================
- Hits        16938    16924      -14     
+ Misses       4934     4922      -12     
+ Partials     1283     1270      -13     

Flag	Coverage Δ
experimental-codecov	73.04% <97.67%> (+0.04%)	⬆️
stable-codecov	68.04% <97.67%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

[technicallyty]

lgtm

[robert-zaremba]

Why we are removing oneof? Can we use blake3 instead?
PS: I thought we want to update proto first (before updating code) ;)

[ryanchristo]

Why we are removing oneof?

We are removing oneof because it breaks amino signing, i.e. "This pull request updates ContentHash to no longer use oneof, which breaks amino signing".

Can we use blake3 instead?

That's being discussed in #248 and would be a separate pull request.

PS: I thought we want to update proto first (before updating code) ;)

That's the process for new features that are in the design phase. I don't think it's necessary when fixing an existing feature but maybe that's something we can further discuss. Seems unnecessary for the change here or adding queries.

[aleem1314]

Lgtm