feat: print each error within AggregateErrors

[gaurav0107]

PR Checklist

• Addresses an existing open issue: fixes 🚀 Feature: Support printing each error within AggregateErrors #4982
• That issue was marked as status: accepting prs
• Steps in CONTRIBUTING.md were taken

Overview

When a test throws an AggregateError, reporters only printed the top-level message and stack; the individual errors in error.errors were dropped. This extends getFullErrorStack in lib/reporters/base.js to traverse err.errors and append each contained error (message + stack), reusing the same recursive formatting as the existing err.cause trail.

• Nested aggregates and cause chains inside aggregated errors render via the same recursion.
• Non-Error entries (an AggregateError may be constructed with any iterable) are stringified rather than crashing the reporter.
• Circular references are guarded by the existing seen set.

Output for an AggregateError:

  1) test:
     AggregateError: 2 things went wrong
      <stack>
     Aggregated error: Error: first failure
      <stack>
     Aggregated error: TypeError: second failure
      <stack>

Unit tests added in test/reporters/base.spec.cjs cover multiple/single/non-Error/nested/circular cases.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.42%. Comparing base (7ad398e) to head (f8e0524).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6120      +/-   ##
==========================================
+ Coverage   82.38%   82.42%   +0.03%     
==========================================
  Files          61       61              
  Lines        4564     4574      +10     
  Branches      958      964       +6     
==========================================
+ Hits         3760     3770      +10     
  Misses        804      804              

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