The main goal here is to make the function pointers comptime, so that we
don't have to do the crazy stuff with async function frames.
Since InStream, OutStream, and SeekableStream are already generic
across error sets, it's not really worse to make them generic across the
vtable as well.
See #764 for the open issue acknowledging that using generics for these
abstractions is a design flaw.
See #130 for the efforts to make these abstractions non-generic.
This commit also changes the OutStream API so that `write` returns
number of bytes written, and `writeAll` is the one that loops until the
whole buffer is written.
Added Buffer.initCapcity() to buffer to allow preallocation of a block of memory to reduce future allocations. Uses the added ArrayList.initCapacity() function to achieve this.
Added Buffer.capacity() to track current usable allocation size, not counting null byte, and returning 0 if empty or created with Buffer.initNull()
Added a test for initCapacity() that shows that no further allocation is performed for an append of size smaller than or equal to capacity when initCapacity is used.
Added a test for initSize(), since it did not exist already.
Also added a comment to better explain the difference between initSize() and initCapacity()
note: forgot in the first commit but thanks to mikdusan for helping me brainstorm, through the process, and for drawing up a draft diff which I tweaked.
