GEN-34: deer: implement Content IR

[indietyp]

🌟 What is the purpose of this PR?

This implements Content and related Deserializers, which is one of the last steps needed before we can start on the derive macro.

🚫 Blocked by

• deer: implement Deserialize for tuples #2418

🚀 Has this modified a publishable library?

This PR:

• modifies an npm-publishable library and I have added a changeset file(s)
• modifies a Cargo-publishable library and I have amended the version
• modifies a Cargo-publishable library, but it is not yet ready to publish
• modifies a block that will need publishing via GitHub action once merged
• does not modify any publishable blocks or libraries, or modifications do not need publishing
• I am unsure / need advice

---

• To see the specific tasks where the Asana app for GitHub is being used, see below:
  • https://app.asana.com/0/0/1204596705932088

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (cee1a1b) 52.75% compared to head (56975b2) 56.41%.
Report is 1118 commits behind head on main.

❗ Current head 56975b2 differs from pull request most recent head d3a81a6. Consider uploading reports for the commit d3a81a6 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2434      +/-   ##
==========================================
+ Coverage   52.75%   56.41%   +3.65%     
==========================================
  Files         331      341      +10     
  Lines       27555    26287    -1268     
  Branches      420      421       +1     
==========================================
+ Hits        14538    14829     +291     
+ Misses      13015    11453    -1562     
- Partials        2        5       +3     

Flag	Coverage Δ
backend-integration-tests	3.66% <ø> (-3.69%)	⬇️
unit-tests	1.49% <ø> (+1.49%)	⬆️

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[github-advanced-security]

clippy found more than 10 potential problems in the proposed changes. Check the Files changed tab for more details.

[linear]

GEN-34