Allow Teakra to either own DSP memory or have the user provide their own

[wheremyfoodat]

Continuing from #55

As the title says, this PR lets the user supply their own DSP memory if needed, for purposes such as implementing fastmem, using host shared memory for exposing DSP RAM to other processing, applying memory protections to DSP memory, and so on.

This is done via a UserConfig object via which the user passes to Teakra. This config object will also be needed when it's time to merge the Teak JIT from https://github.com/raphaelthegreat/teakra/ (for enabling/disabling the JIT), which is probably not going to be any time soon as it needs a hefty rewrite.

One minor caveat is that this UserConfig struct hasn't been ported to the C interface yet, and they behave the same as they did before this PR (ie always owning DSP memory). The reason for this is that I'm unsure how to port the struct in the longterm without duplicating a lot of code (by eg making a C version of the struct, and having the interface's cpp file copy each field to the C++ version). Regardless, this isn't a huge problem since the C interface isn't as widely used, and users likely don't care much about this in the first place. It will be more important to implement C interface configs when the JIT is ready.

Tested locally by integrating the changes to Panda3DS, running the test verifier, and by testing the Rust bindings to see that the C interface still works fine.

[wheremyfoodat]

Err, I should probably make CI run tests on pull request

[wwylele]

I think a better way in modern C++ to do this is something like

std::option<std::unique_ptr<std::array<u8, 0x80000>>> raw;
u8* raw_ptr; // points to either raw or user-supplied memory

so when Teakra manages the memory, it doesn't need to manually do new/delete, and it reduce the chance we mishandle and leak it

[wheremyfoodat]

Should be fixed. Skipped the optional since by default unique_ptr is initialized to null and doesn't own any memory.

[wwylele]

You can tell my C++ skills are too rust-y by not thinking about null values 😂