core[patch]: Pass input to invocation for JSON schema tools

[dkundel]

#6306 introduced the ability to pass JSON Schema instead of Zod instances into the schema of tool() or DynamicStructuredTool. This would skip the input validation on the Langchain side but it introduced two bugs that this PR addresses:

1. Even though the tool get appropriately triggered it would always pass {} as input since the fallback Zod schema that was used during initialization would map to z.object({}) which when used with schema.parseAsync(input) results in all properties being dropped. To get around this we need to use passthrough() to tell Zod not to drop any additional properties.
2. The tool() function is checking if a schema is not an object Zod schema and then returns a DynamicTool instance instead of a DynamicStructuredTool instance. This results in the resulting Tool execution always passing undefined as input. Instead tool() needs to check that if the input schema is defined that it's not an instance of a ZodType before checking any other conditions.

This is my first contribution so I'm not sure if I missed anything but the tests seemed to pass.

My Twitter handle is dkundel.

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[jacoblee93]

Thanks for catching! Just ran lint and format but will merge and ship shortly