Fix validate_chain_list() colnames check to compare all chains

[utkarshpawade]

Fixes #528

• Fixed bug where identical(cnames[, 1], cnames[, 2]) only validated colnames of chains 1 and 2, silently ignoring mismatches in chains 3+
• Replaced sapply with lapply + vapply to avoid matrix/list type ambiguity and compare all chains against the first

[Copilot]

Pull request overview

Fixes validate_chain_list() so column-name consistency is validated across all chains (not just chains 1 and 2), preventing silent acceptance of mismatched parameter names/order in chains 3+.

Changes:

• Replaced sapply(x, colnames) simplification logic with lapply(x, colnames) to avoid matrix/list ambiguity.
• Updated the equality check to compare every chain’s colnames() against chain 1 via vapply(..., identical, ...).

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[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 98.67%. Comparing base (62fce06) to head (76c8db6).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #529      +/-   ##
==========================================
- Coverage   98.71%   98.67%   -0.04%     
==========================================
  Files          35       35              
  Lines        5903     5901       -2     
==========================================
- Hits         5827     5823       -4     
- Misses         76       78       +2     

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