fix(grpc): handle union shared fields

[meskill]

Summary:
Pr to address differences in async_graphql and jit engines related to selecting shared fields from union type.

I've checked other graphql implementations and it appeared that original test should not work actually based on spec. So this pr:

• generates shared interface for oneOf for proto config generator
• test now uses interface fragment to select shared fields
• improve jit implementation for tests to handle interfaces on fragments

Issue Reference(s):
Fixes #... (Replace "..." with the issue number)

Build & Testing:

• I ran cargo test successfully.
• I have run ./lint.sh --mode=fix to fix all linting issues raised by ./lint.sh --mode=check.

Checklist:

• I have added relevant unit & integration tests.
• I have updated the documentation accordingly.
• I have performed a self-review of my code.
• PR follows the naming convention of <type>(<optional scope>): <title>

[codecov]

Codecov Report

Attention: Patch coverage is 98.85057% with 1 line in your changes missing coverage. Please review.

Project coverage is 86.33%. Comparing base (aa669c4) to head (8a39bf6).
Report is 1 commits behind head on main.

Files	Patch %	Lines
src/core/ir/resolver_context_like.rs	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2757      +/-   ##
==========================================
+ Coverage   86.21%   86.33%   +0.11%     
==========================================
  Files         255      255              
  Lines       25105    25155      +50     
==========================================
+ Hits        21645    21717      +72     
+ Misses       3460     3438      -22     

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