fix: properly handle nested objects when building query params

[Melchyore]

This PR fixes an issue where passing an object in the query parameters generated an invalid query string.

Previous behavior

When sending a query like:

const data = await client.api.admin.products.$get({
  query: {
    filter: {
      format: 'foo'
    }
  }
})

the generated query string was:
?filter=[object Object]

New behavior

Objects are now correctly expanded into key-value pairs:

?filter[format]=foo

Nested objects support

The fix also adds support for nested objects:

const data = await client.api.admin.products.$get({
  query: {
    filter: {
      name: { like: 'foo' },
      price: { gte: 1200 }
    }
  }
})

Generates the correct query string:
?filter[name][like]=foo&filter[price][gte]=1200