feat: multi variable tools

[ ] Read the Contributing documentation.
[ ] Read the Code of conduct documentation.
[ ] Name your Pull Request title clearly, concisely, and prefixed with the name of the primarily affected package you changed according to Good commit messages (such as memory: add interfaces for X, Y or util: add whizzbang helpers).
[ ] Check that there isn't already a PR that solves the problem the same way to avoid creating a duplicate.
[ ] Provide a description in this PR that addresses what the PR is solving, or reference the issue that it solves (e.g. Fixes #123).
[ ] Describes the source of new concepts.
[ ] References existing implementations as appropriate.
[ ] Contains test coverage for new functions.
[ ] Passes all golangci-lint checks.

tmc / langchaingo