Various memory/efficiency improvements for control/PCM ROM loader

[dwhinham]

std::vector is a container which can trigger requests for more memory from the operating system every time its heap-allocated storage is filled. When performing thousands of push_back() operations, this can result in many expensive calls to malloc()/free() (and copy/move operations) behind the scenes, as larger chunks of memory are requested, data is moved from the old location to the new location, and the old location is freed.

On modern machines with operating systems that provide sophisticated memory allocators, memory fragmentation isn't a problem and we can get away with this.

However, on embedded/baremetal systems which aren't able to avoid memory fragmentation, this can cause problems, so we should try to avoid unnecessary reallocations by reserving the space up-front whenever it is known.

This PR reduces overall memory allocations inside libemusc.so from ~13000 to ~3000 as shown by the following heaptrack trace:

There are probably more places where this can be improved further, but this should take care of the low-hanging fruit.

Cheers!

[skjelten]

Nice and clean, thanks a lot!