Refactor Prophet struct to prevent invalid states

[coderabbitai]

The TODO comment in crates/augurs-prophet/src/prophet.rs suggests moving certain fields into a separate struct. Refactoring these fields can minimize the number of optional fields in the Prophet struct and reduce the risk of the struct being in an invalid state due to improper combinations of optional fields.

This issue was raised in PR #118.

PR URL: #118
Comment URL: #118 (comment)

Requested by @sd2k.