Update the buffer API

[andrevidela]

• I have read CONTRIBUTING.md.
• I have checked that there is no existing PR/issue about my proposal.
• I confirm that this contribution did not involve GenerativeAI nor Large Language Models.

Summary

The buffer API has the following problems:

• No way to create an empty buffer
• No way to grow a buffer in-place
• Additional overhead when creating a newBuffer due to Maybe

The proposal

Add the following

allocBuffer : Int -> IO Buffer
allocBuffer n = primtIO $ prim__newBuffer n

emptyBuffer : IO Buffer
emptyBuffer = allocBuffer 0

resize : Buffer -> Int -> IO ()

grow : Buffer -> Int -> IO ()
grow b n = resize b (!(rawSize b) + n)

-- same as newBuffer but without Maybe
nonEmptyBuffer : (n : Int) -> {0 auto notZero : n /= 0} -> IO Buffer