[WIP] Rewriting the Univariate Solver

This PR aims to rewrite a cleaner and robust univariate equation solver.
- [ ] Univariate
    - [x] polynomial
    - [x] rational
    - [ ] trigonometric
    - [ ] functions with exp and log
- [ ] Multivariate
A solver for radical equations, it helps in solve equations like https://github.com/sympy/sympy/pull/7523/files#diff-4faca8d7a25abee5a1b817be0ecdafe0R243.