Support of slice for Program code

[ibuki2003]

Now Program::code is ArrayVec type, which contains its own data.
I think almost all of use cases are to program "static" one, and it is not necessary to allocate memory every time.

So I suggest to add slice support for Program::code.

Furthermore, I want pio_proc assembler macros to support slice as well.
The macros returns ProgramWithDefines<> type, which has dynamic type parameter, so it is not possible to use it as static variable.

I am able to work with this change, but I am not sure if it is good idea or not.

[jannic]

As pio programs are only a few bytes long, I wonder if it's worth to spend effort on optimizing memory usage.
Do you have an example where such a change would help?

[ibuki2003]

Hello, @jannic.

Your indication is correct; the performance problem is not so significant.
I don't like that the process is not minimal.

However, I think that is more convenient since slice is available as a primitive type.

• In almost all use cases, the program is a static value, so we can use a static slice.
  • The difference is little, but a simple and fast way is preferable.
• When dynamically generating programs, we don't need to convert the array to ArrayVec.

---

The code I first confront this issue is like this:

fn main() {
  //
  pio0.install(&PROGRAM).unwrap();
  //
}

// Here the program is compile-time-static value
// but this approach is not available.
static PROGRAM: Program<32> = pio_proc::pio_asm![
  ".wrap_target",
  "  set pins, 1",
  "  set pins, 0",
  ".wrap",
].program;

I get some errors because ArrayVec does not work in statics.