Make a bunch of functions const

[AhoyISki]

Hello

In std, Vec::new() is a const function. To me, it seems unexpected that Gapbuffer::new() is not a const function. This also prevents some useful statements like

static MUTEX = Mutex<GapBuffer<u8>> = Mutex::new(GapBuffer::new());

Instead, because of the non constness of GapBuffer::new(), you are forced to write:

static MUTEX: LazyLock<Mutex<GapBuffer<u8>>> = LazyLock::new(Mutex::default);

Which not only is more of a mouthful, in theory it is also slower, because of the LazyLock part.

[AhoyISki]

Also, it'd be nice if this coincided with a new version on crates.io.