fix(sessions): change numbers to strings in the `userOperation`

[geekbrother]

Description

This PR changes numbers to strings in the userOperation to support bigint at the JS side which should be the string.

How Has This Been Tested?

• Manually tested by calling the pre-created cosign request.

Due Diligence

• [ ] Breaking change
• [ ] Requires a documentation update
• [ ] Requires a e2e/integration test update