Support for inline struct fields

[m4tty-d]

Hey!

I just ran into that the current implementation doesn't properly handle inline struct fields.

When a struct embeds another struct with the json:",inline" tag, the fields from the embedded struct should be flattened into the parent struct's schema.

Here's a test case that demonstrates the issue:

func TestInlineStructField(t *testing.T) {
	type TestInline struct {
		InlineField1 string  `json:"inlineField1"`
		InlineField2 *string `json:"inlineField2,omitempty"`
	}

	type Test struct {
		*TestInline `json:",inline"`
		TestField   string `json:"testField"`
	}

	assert.Equal(t,
		`export const TestSchema = z.object({
  inlineField1: z.string(),
  inlineField2: z.string().optional(),
  testField: z.string(),
})
export type Test = z.infer<typeof TestSchema>

`, StructToZodSchema(Test{}))
}

I've already created a fix, will open a pull request soon.