feat(Cabal, cabal-install): Display -O and -g as numeric levels instead of booleans

[zlonast]

This PR improves the handling of the debug-info and optimization field to ensure consistency between its configuration and CLI representations.

Changes

• Config default: Updated the serialization logic to represent the default NoDebugInfo value as 0 instead of False in ~/.config/cabal/config.
• Internal consistency: Aligned the default DebugInfoLevel between pkgHashDebugInfo and the Parsec instance. This resolves potential inconsistencies when processing manually generated configuration files.
• Parsing fix: Fixed a bug where boolean flags were not being correctly parsed for the debug-info field. The parser now properly handles both boolean and integer inputs.

    -- TODO: [code cleanup] The following is a hack. The "optimization" and
    -- "debug-info" fields are OptArg, and viewAsFieldDescr fails on that.
    -- Instead of a hand-written parser and printer, we should handle this case
    -- properly in the library.

    -- TODO: The following is a temporary fix. The "optimization"
    -- and "debug-info" fields are OptArg, and viewAsFieldDescr
    -- fails on that. Instead of a hand-written hackaged parser
    -- and printer, we should handle this case properly in the
    -- library.

---

Template Α: This PR modifies behaviour or interface

Include the following checklist in your PR:

• Patches conform to the coding conventions.
• Any changes that could be relevant to users have been recorded in the changelog.
• Tests have been added. (Ask for help if you don’t know how to write them! Ask for an exemption if tests are too complex for too little coverage!)

[Mikolaj]

@ffaf1 notices this seems to change the behaviour of cabal (namely, it's output). If so, a different PR template should be used, which asks for a different set of tasks.

Would it be possible to add a test that prints the -O and -g things? Preferably in an early commit, so that it illustrates the modification, showing how it requires a change in the test result.