fix(checkpoint-validation): fix broken initial release

[benjamincburns]

Unfortunately the initial release of @langchain/langgraph-checkpoint-validator is broken for two reasons.

1. A bug in @swc-node/register attempts to resolve SWC packages from the CWD rather than the installed package's node_modules directory.
2. The jest config used by the CLI wasn't included in the release because I forgot to add it to the files array in package.json.

I fixed the first issue by applying the workaround mentioned here: swc-project/swc-node#805 (comment).

I fixed the second issue by moving the runtime jest config into the src dir and making it a TS file.

I tested this locally using npm link and it seems to fix both issues.

Sorry for the hiccup!

[jacoblee93]

Thank you!