config: support backslash-newline line continuation (#611)

[Mobeen0119]

Add backslash-newline line continuation to config parser.

O(n) two-pointer approach.
Handles Unix (\n) and Windows (\r\n) line endings.

Example:
CMDLINE: root=/dev/sda1 rw quiet
zswap.enabled=0

Becomes one continuous line.

Tested with 20 unit tests + 100K fuzz + 50K comparisons vs old code.

Fixes #611

Test Files :
test_compare.c
test_full.c

[programmerlexi]

This is the third time you have created this PR. Can you please just amend/rebase new changes and force push them instead of recreating the PR everytime?

[CherrieTheShifter]

Yes This Please 🙏

[Zesko]

I would suggest improving performance when limine.conf contains many lines.

It should skip lines that don't contain kernel command lines instead of checking every single line.
Otherwise, checking all lines can unnecessarily increase boot time on large configurations.

[Mobeen0119]

This pipeline already runs multiple full-buffer passes before mine (hash check, continuation-collapse, whitespace trim, macro load, macro expand), so mine isn't adding a new category of cost and skipping non-cmdline lines isn't possible at this point since nothing's tokenized into lines yet. Worth noticing: the whitespace-trim loop right after mine is actually O(n²), not O(n) ... it shifts the entire remaining buffer on every skip event, which is the bigger perf risk on large configs, and it's pre-existing.