fix: Complete array attribute serialization for all payload types

[tippmar-nr]

Description

PR #3456 added array serialization in JsonSerializerHelpers but missed two code paths:

1. GenericConverter (AttributeDefinition.cs): No IEnumerable case — arrays fell through to ToString(), producing garbage like System.Int32[] in transaction traces and events.
2. AttributeValue.SetValue (Segments/AttributeValue.cs): The protobuf-backed AttributeValue for span events had no IEnumerable handling — arrays fell through to TypeCode.Object → ToString()→ garbage strings.

Changes

• GenericConverter: Added IEnumerable case with recursive element conversion and null filtering
• Segments/AttributeValue: Added _arrayValue field and IEnumerable handling in SetValue; updated Value getter to return array data
• Unit tests: GenericConverterTests (11 new), EventWireModelSerializerTests (5 new)
• Composite tests: Updated Assertions.HaveSameValue for IEnumerable element-wise comparison; added SpanCustomAttributes_WithArrays test
• Integration tests: Array attribute assertions for transaction traces, transaction events, and span events

Fixes #3530

[codecov-commenter]

Codecov Report

❌ Patch coverage is 95.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 81.78%. Comparing base (3e94fb9) to head (400ede0).

Files with missing lines	Patch %	Lines
...ent/NewRelic/Agent/Core/Segments/AttributeValue.cs	88.88%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3531      +/-   ##
==========================================
- Coverage   81.79%   81.78%   -0.02%     
==========================================
  Files         508      508              
  Lines       34345    34365      +20     
  Branches     4061     4067       +6     
==========================================
+ Hits        28092    28104      +12     
- Misses       5285     5290       +5     
- Partials      968      971       +3     

Flag	Coverage Δ
Agent	82.76% <95.00%> (-0.02%)	⬇️
Profiler	71.75% <ø> (ø)

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

Files with missing lines	Coverage Δ
...Relic/Agent/Core/Attributes/AttributeDefinition.cs	88.21% <100.00%> (+0.48%)	⬆️
...ent/NewRelic/Agent/Core/Segments/AttributeValue.cs	76.66% <88.88%> (+1.35%)	⬆️

... and 1 file with indirect coverage changes

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