Read BTF alone in rk btf and write qualifiers in one order

[tamnd]

Two things the first run of rk btf on real pahole output showed, on a test file built with gcc-14 and rucc for arm64 and encoded with pahole --btf_encode_detached.

rk btf now reads a file that is BTF alone, which is what pahole --btf_encode_detached writes and what /sys/kernel/btf/vmlinux is, besides an ELF file with a .BTF section. pahole needs llvm-objcopy to add the section itself, so detached BTF is the easy way to compare single objects.

A run of const, volatile and restrict is now written in one order. gcc describes const volatile int as volatile over const and rucc as const over volatile, which means the same type and should not be a finding.

The rest of what the run found is rucc's DWARF and goes to tamnd/rucc: base type names (unsigned long where gcc says long unsigned int), a typedef lost in a function pointer's return type, multi-dimensional arrays nested instead of one array type with several subranges, and typedefs nothing uses.

Part of #6 and #7.