fix(tests): fix all failing tests

[BrendanC23]

1. Remove /\\. from vitest.config.ts. This was necessary to fix the error No test files found. This can also be fixed by updating Vitest to version 4, but this has a change to how snapshots are stored. See the migration guide. All of the tests are found by removing /\\., so the Vitest upgrade is better in a later PR.
2. Inlined z in vitest.config.ts to spy on parse() from zod/v4/core. Without this, a TypeError: Cannot redefine property: parse error occurs.
3. Change bun test to bun run test in CONTRIBUTING.md. bun test runs Bun's native test runner, not the test script.
4. Add Test stage to .github/workflows/main.yml. It was removed in this PR and the tests haven't been running in CI.
5. Fix failing tests

Notes:

1. All
   • Fixed tests that called useForm outside of a component. This fixed the errors Error: Invalid hook call. Hooks can only be called inside of the body of a function component. and TypeError: Cannot read properties of null (reading 'useRef').
2. Arktype
   • This PR changed from directly calling Arktype to using standard schema. Part of this transition was changing type: error.code to type: '' (because error.code is not part of the standard schema). This required an update to the snapshot.
3. Superstruct
   • Fix validation of schemas that perform coercion ({ coerce: true } must be passed in)
   • Added additional overload for type definition superstructResolver that improves handling of coerced schemas (This fixes a type error with the form values).
   • Fix definition of coercion schema so that it correctly converts from number to string
   • As mentioned in this issue, there is no way to infer the input type of a coerced schema. A separate PR would be necessary. Some of the type inference tests have been changed to manually provide the input type (this enables watch to return the correct value for a coerced schema).
4. Typeschema
   • The for loop was looping through the schemaErrors variable, but the current error was based on the typeschemaErrors[0] variable. This caused only the first error to be returned.
   • Change from spying on typeschema.validate to watching schema["~standard"]
5. Zod
   • Fixed Zod tests that spied on schema.parse() instead of z4.parse()
   • Added missing snapshots

Fixes #832