Function with_arena 

pub fn with_arena<F, R>(f: F) -> R
where
    F: FnOnce(&Bump) -> R,

Execute a function with access to the thread-local arena

This is used by CemString to allocate strings from the arena.

Performance

~5ns vs ~100ns for global allocator (20x faster)

Example

let arena_str = with_arena(|arena| arena.alloc_str("Hello"));