Stack overflow error when opening large CSV files ("Maximum call stack size exceeded")

[xXLeoXxOne]

Description

Opening CSV files with many rows causes the extension to crash with RangeError: Maximum call stack size exceeded.

Stack trace:

RangeError: Maximum call stack size exceeded
    at CsvEditorController.getEffectiveHeader (CsvEditorProvider.js:691:33)
    at CsvEditorController.updateWebviewContent (CsvEditorProvider.js:528:34)
    at CsvEditorController.resolveCustomTextEditor (CsvEditorProvider.js:66:14)
    ...

Steps to reproduce

1. Open a file with a very large number of rows (see energy_train.csv)
2. Observe the error

Root Cause

The extension uses Math.max(...array) spread syntax in multiple locations to calculate the maximum column count.
When the CSV has many rows, spreading the array into Math.max() exceeds JavaScript's call stack limit (~65K arguments).

Fix suggestion

Use a stack-safe approach through using reduce()