refactor: replace byte-swap macros with static inline functions

[hugo-hur]

The ltfs_betou*/ltfs_u*tobe macros cast byte buffers to uint16_t/uint32_t and dereferenced them, e.g. *(uint32_t *)(buf). Callers pass buffers at arbitrary offsets (cdb + 3, coh_data + 6), so these were unaligned accesses and causes undefined behaviour that happens to work on x86 but faults or returns rotated/garbage data on alignment-strict CPUs. Convert each to a static inline function that moves bytes through memcpy, which is well defined for any alignment and lowers to a single load/store plus byte swap without runtime cost.

Using functions instead of macros also:

• Adds real type checking: parameters and return values have concrete types (void */const void * buffers, fixed-width integers) instead of textual substitution, so passing the wrong type is caught at compile time rather than silently reinterpreted.
• Produces clearer compiler errors: diagnostics point at the call site and the function signature instead of deep inside a macro expansion.
• Evaluates each argument exactly once and needs no defensive parentheses, removing the double-evaluation and operator-precedence hazards that the old ltfs_betou64 macro had.

The signatures are unchanged, so all call sites are untouched. Add <stdint.h> and <string.h> so the header is self-contained.

Summary of changes

• Change byte-swap endianness macros into static inline functions

Type of change

• Refactoring

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings