feat(sterni/blipqn): reuse address and socket for multiple Sends

This is achieved by storing the resources we need to acquire for
interacting with the flipdot (socket fd and addrinfo struct) in a
`struct flipdot` that is dynamically allocated and treated as an opaque
pointer object via the BQN FFI.

To make sure these resources are released correctly, we only provide a
lisp style WithFlipdot to the user which takes care of acquiring and
releasing the `struct flipdot`. This works even if an error occurs in
the function the user provides thanks to _defer_. I'm not sure if
calling it _defer_ is right since Go's error handling works differently,
so defer really is deferred execution in a sense which doesn't really
fit what we're doing here. The closest is probably Haskell's bracket,
but that name references it's triadic nature which doesn't fit our
implementation.

Change-Id: Iff65d277a448dbe0c6ac93e816ece5ab6fa10190
Reviewed-on: https://cl.tvl.fyi/c/depot/+/13011
Reviewed-by: sterni <sternenseemann@systemli.org>
Tested-by: BuildkiteCI

users/sterni/blipqn/examples.bqn

@@ -1,6 +1,6 @@
 #!/usr/bin/env BQN
 
-⟨MakeFlipdot⟩ ⇐ •Import "../lib/"⊸∾⍟("bin" (⊣≡(-∘≠⊸↑)) •path) "blipqn.bqn"
+⟨WithFlipdot⟩ ⇐ •Import "../lib/"⊸∾⍟("bin" (⊣≡(-∘≠⊸↑)) •path) "blipqn.bqn"
 
 examples ← ⍉>⟨
 "random"‿{𝕩.Send 𝕩.shape •rand.Range 2},
@@ -19,11 +19,9 @@ opts ← {
   host‿port‿width‿height‿example ← •args
 
   example ⇐
-  addr ⇐ host⋈•ParseFloat port
-  dim ⇐ •ParseFloat¨ width‿height
+  cfg ⇐ ⟨host⟩∾•ParseFloat¨ port‿width‿height
 }
 
 action ← examples (⊏⊸(⊑∘⊐) ⊑ ⊏˜⟜1)⟜< opts.example
 
-flip ← opts.addr MakeFlipdot opts.dim
-Action flip
+opts.cfg WithFlipdot action