The ISchema interface is missing declarations for isValid and isValidSync.

[oarodrig]

Describe the bug
The ISchema interface is missing the isValid and isValidSync methods. This makes functions like reach harder to use, as those methods can't be called on the resulting ISchema. I think it makes sense for both of those methods to be present on the interface.

To Reproduce

See https://codesandbox.io/p/sandbox/zealous-bird-wvyxzt?file=%2Fsrc%2Findex.test.ts

Expected behavior
isValid and isValidSync are available for use from the ISchema interface.

Platform (please complete the following information):

• Browser - Firefox
• Version - 123.0.1 (64-bit)