warp: fix batch pump stalls - #172

Both drivers build jsaddle-warp from the PR head
(2152422657602dc29c89140cebd3d7fae080acf1) via source-repository-packages
until upstream releases it: nix/lib.nix covers projects that inherit
obeliskLib.source-repository-packages, and lib/project.nix covers the
obelisk library release itself (reflex-dom +use-warp). jsaddle core
stays on Hackage; the patch is jsaddle-warp-only.

cabal check rejects an unbounded base (missing-bounds-important), which
fails every Haskell-CI job since #172.

#173: jsaddleWebViewInvalidate takes the shared wkWebViewBatchLock before
closing a context, so invalidating mid round trip no longer orphans the
lock and freezes every other window — what per-window teardown needs.
#172: jsaddle-warp sends batches off the batch pump, so a slow WebSocket
no longer stalls the page.  cabal.project + both flake.nix sites +
flake.lock.