fix: ORM IndexKeyCodec (#475)

[ruhatch]

Description

Dynamically lengthed IndexKeyCodecs suffered from the same prefixing issue that we identified in #456. This PR fixes that issue by introducing a default key codec that can be used for building both primary keys and secondary index keys.
Key parts, except the last part, follow these rules:

• []byte is encoded with a single byte length prefix
• strings are null-terminated
• integers are encoded using 8 byte big endian.

Closes: #475

---

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 #525 (aa74351) into master (39a0491) will decrease coverage by 0.24%.
The diff coverage is 77.67%.

❗ Current head aa74351 differs from pull request most recent head a652622. Consider uploading reports for the commit a652622 to get more accurate results

@@            Coverage Diff             @@
##           master     #525      +/-   ##
==========================================
- Coverage   75.92%   75.68%   -0.25%     
==========================================
  Files         104      103       -1     
  Lines       14146    14204      +58     
==========================================
+ Hits        10741    10750       +9     
- Misses       2783     2808      +25     
- Partials      622      646      +24     

Flag	Coverage Δ
experimental-codecov	75.68% <77.67%> (-0.25%)	⬇️
stable-codecov	67.19% <77.67%> (-0.25%)	⬇️

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

[likhita-809]

@ruhatch can you fix the failing checks?

[blushi]

After some discussions, this is not actually ready for review yet, will set it back to draft.

[clevinson]

@blushi just to confirm- this is not blocking Baikal correct?

aka - does this work resolve a bug that directly affects x/ecocredit module's use of the orm package? Or is it resolving a bug in orm that doesn't affect x/ecocredit module?

[blushi]

@clevinson No this is not blocking Baikal, this will fix secondary indexes encoding, and x/ecocredit doesn't use secondary indexes atm.

[ruhatch]

Looks good overall. I can't see a better way to do indexing API right now, but we can keep thinking about it I guess.

[amaury1093]

lgtm. First time seeing this code, so not super familiar, would ideally like another approval from someone else.

[likhita-809]

looks great.
can you address @AmauryM 's comments, since I have similar concerns ?