Create a method that formats a list of strings into a formatted string with custom separators and brackets.

Examples:

Input: strings = ["Hello", "World"], separator = " | ", addBrackets = true
Output: "[Hello | World]"
Explanation: The strings are joined with the custom separator and wrapped in brackets.

Input: strings = ["a", "b", "c"], separator = " - ", addBrackets = false
Output: "a - b - c"
Explanation: The strings are joined with the custom separator without brackets.

Input: strings = ["Single"], separator = ", ", addBrackets = true
Output: "[Single]"
Explanation: Even single items get brackets when requested.
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