feat(js/fows): added schemaMode option on flows (and other actions) to control schema behavour

[pavelgj]

Right now we only validate, but if the schema has defaults or transforms those don't get applied. Ex:

  const testFlow = ai.defineFlow(
    {
      name: 'testFlow',
      inputSchema: z.object({
        foo: z.string().default('default foo'),
      }),
      outputSchema: z.object({
        input: z
          .object({
            foo: z.string().optional(),
          })
          .optional(),
        bar: z.string().transform((val) => `${val}-transformed`),
      }),
      schemaMode: 'parse',
    },
    async (input) => {
      return { input, bar: 'bar' };
    }
  );

  const result = await testFlow({} as any);

  assert.deepStrictEqual(result, {
    bar: 'bar-transformed',
    input: {
      foo: 'default foo',
    },
  });

also can set schemaMode: 'none', this might be useful in production mode to improve performance in case of large inputs/outputs.

Checklist (if applicable):

• PR title is following https://www.conventionalcommits.org/en/v1.0.0/
• Tested (manually, unit tested, etc.)
• Docs updated (updated docs or a docs bug required)