lexical-core has multiple soundness issues

Summary

`RUSTSEC-2024-0377` contains multiple soundness issues: 1. [Bytes::read() allows creating instances of types with invalid bit patterns](https://github.com/Alexhuszagh/rust-lexical/issues/102) 1. [BytesIter::read() advances iterators out of bounds](https://github.com/Alexhuszagh/rust-lexical/issues/101) 1. [The `BytesIter` trait has safety invariants but is public and not marked `unsafe`](https://github.com/Alexhuszagh/rust-lexical/issues/104) 1. [`write_float()` calls `MaybeUninit::assume_init()` on uninitialized data, which is is not allowed by the Rust abstract machine](https://github.com/Alexhuszagh/rust-lexical/issues/95) 1. [`radix()` calls `MaybeUninit::assume_init()` on uninitialized data, which is is not allowed by the Rust abstract machine](https://github.com/Alexhuszagh/rust-lexical/issues/126) Version 1.0 fixes these issues, removes the vast majority of `unsafe` code, and also fixes some correctness issues.