mach0 refactoring

[wargio]

Mach0 is currently implemented with many quirks, where the buffer is parsed many times.

Probably the author tried to optimize the loading by consuming less memory in favor of slower loading; this leads to many weird parsing patterns scattered across the code where structures are not kept in memory, but instead parsed and freed multiple times, where some functions do the same job but with slightly different results.

Examples:
https://github.com/rizinorg/rizin/blob/dev/librz/bin/format/mach0/mach0.c#L353
https://github.com/rizinorg/rizin/blob/dev/librz/bin/format/mach0/mach0.c#L1423