Core/Movie: Use fmt where applicable

[lioncash]

This is split into its own PR, as it makes mild changes to some of the internal functions in Movie.cpp (namely changing u8 parameters to u32), and not purely replacing StringFromFormat calls.

While u8 may have been OK with printf-style formatting, which promotes most smaller types back to int internally, this won't work with fmt. fmt preserves the type of the passed in arguments, meaning that u8, being an alias of uint8_t (itself being an alias of unsigned char on all the platforms we support), will print out as a character, not a numeric value.

Because of that, we amend some functions to operate on u32 values for two reasons:

1. We actually want said parameters to print out as a value, not a character, and casts are gross.

2. Arithmetic on unsigned types smaller than unsigned int will actually promote to an int, not unsigned int. This is very non-obvious to some and makes for error-prone code. < sizeof(int) types are great for storage, not so much for performing unsigned arithmetic, despite the unsignedness of the type.

[leoetlino]

Hmm, doesn't fmt explicitly print unsigned char and uint8_t as a number, and not a character? fmtlib/fmt#217

[lioncash]

Ah good, I didn't know that was fixed. That'll make future changes less concerning :)

I'll keep the change as is though, since we're still implicitly truncating from int to u8 in our current code.

[Warepire]

Additionally at least on some arches unnecessarily restricting memory usage will generate more complex assembly to access those variables, increasing the size of the binary. ARM64 is one example.

(Just one more reason to get rid of pointless u8's)