Optimizer: simplify expression optimizer rule

[universalmind303]

Is your feature request related to a problem? Please describe. Most other rule based execution engines have some form of expression simplification.

Some common optimizations

• inline constant expressions such as 2+2 - 4
• simplifying boolean logic true = true - true

Additional context other rust based examples

• datafusion: https://github.com/apache/arrow-datafusion/blob/888504a8da6d20f9caf3ecb6cd1a6b7d1956e23e/datafusion/optimizer/src/simplify_expressions/expr_simplifier.rs
• polars: https://github.com/pola-rs/polars/blob/71495ebb017aacc9bedc9723e33481b2307ac8cd/crates/polars-plan/src/logical_plan/optimizer/simplify_expr.rs

[universalmind303]

it seems like some of these expression simplifications happen in other optimizers

One example is combining conditional logic for filters as tested here

https://github.com/universalmind303/Daft/blob/158291c66e03be9b2252a428f826b6e78c2fb30a/src/daft-plan/src/logical_optimization/rules/push_down_filter.rs#L351

[samster25]

Good call out!