feat: Add array concatenation support to concat function

[EeshanBembi]

Fixes #18020

Summary

Enables concat function to concatenate arrays like array_concat while
preserving all existing string concatenation behavior.

Before:

SELECT concat([1, 2, 3], [4, 5]);
-- Result: [1, 2, 3][4, 5]  ❌

After:

  SELECT concat([1, 2, 3], [4, 5]);
  -- Result: [1, 2, 3, 4, 5]  ✅

Implementation

• Extended concat function signature to accept array types
• Added type detection in invoke_with_args() to delegate array operations to Arrow
  compute functions
• Enhanced type coercion to handle mixed array types and empty arrays
• Maintains full backward compatibility with string concatenation

Test Coverage

• ✅ Array concatenation: [1,2] + [3,4] → [1,2,3,4]
• ✅ Empty arrays: [1,2] + [] → [1,2]
• ✅ Nested arrays: [[1,2]] + [[3,4]] → [[1,2],[3,4]]
• ✅ String concatenation unchanged: 'hello' + 'world' → 'helloworld'
• ✅ Mixed type coercion: true + 42 + 'test' → 'true42test'
• ✅ Error handling: [1,2] + 'string' → Error

Approach Benefits

Function-level implementation vs planner replacement:

• Cleaner architecture (single responsibility)
• No planner complexity
• Better performance
• Easier testing and maintenance