Improve detector for incorrect-exponentiation and include new test-cases

[arturoBeccar]

Description

• [x] Improve detector incorrect-exponentiation to detect test-cases where the symbol ^= is used.
• [x] Also add new relevant vulnerable and remediated test cases for using this symbol.
• [x] Add, if necessary, any relevant additional documentation for the detector and test cases.
• [x] Ensure that other than incorrect-exponentiation and maybe soroban-version, all other issues detected by scout are not present in the code.