refactor: destroy spawn of satan type punning in ETF parser

[braindigitalis]

This removes two instances of type punning in the ETF parser. Please take note of the comments added to the function etf_parser::process_atom(). This is a performance hotspot and any changes to this function should be carefully profiled.

Code change checklist

• I have ensured that all methods and functions are fully documented using doxygen style comments.
• My code follows the coding style guide.
• I tested that my change works before raising the PR.
• I have ensured that I did not break any existing API calls.
• I have not built my pull request using AI, a static analysis tool or similar without any human oversight.

[Mishura4]

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