deer: add *Access::context()

[indietyp]

🌟 What is the purpose of this PR?

This PR adds ArrayAccess::context() and ObjectAccess::context() which roughly are equivalent to DeserializeSeed in serde. This enables inner methods of ArrayAccess and ObjectAccess to modify/access the context, but also call other deserializers (like NoneDeserializer)

🔗 Related links

• need was discovered in deer: introduce StructVisitor #2437

🚀 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

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.

Project coverage is 56.38%. Comparing base (fa4ff75) to head (332c7da).
Report is 3021 commits behind head on main.

Files with missing lines	Patch %	Lines
libs/deer/json/src/lib.rs	0.00%	6 Missing ⚠️
libs/deer/desert/src/array.rs	0.00%	3 Missing ⚠️
libs/deer/desert/src/object.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2443      +/-   ##
==========================================
- Coverage   56.41%   56.38%   -0.03%     
==========================================
  Files         341      341              
  Lines       26287    26299      +12     
  Branches      421      421              
==========================================
  Hits        14829    14829              
- Misses      11453    11465      +12     
  Partials        5        5              

Flag	Coverage Δ
backend-integration-tests	3.66% <ø> (ø)
deer	68.71% <0.00%> (-0.22%)	⬇️
unit-tests	1.49% <ø> (ø)

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