feat(lisp/klatre): Add klatre, a grab-bag lisp util package

Add Klatre, a grab-bag common lisp utility package, including
definitions for `comment`, `posp`, `chunk-list`, and `mapconcat`.

The name traces its lineage back to Abseil, a similar grab-bag utility
library for C++ - abseiling is what you do to go down a route after
you're done climbing it, and klatre is norwegian for "to climb"

Change-Id: I5efd91d8af827883679ce1a2eed3229b28e082ac
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1346
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>

lisp/klatre/default.nix

@@ -0,0 +1,10 @@
+{ depot, ... }:
+
+depot.nix.buildLisp.library {
+  name = "klatre";
+
+  srcs = [
+    ./package.lisp
+    ./klatre.lisp
+  ];
+}