feat(performance): Always inline certain small methods

[vezenovm]

Description

Problem*

Part of general effort to reduce Brillig bytecode sizes and execution trace

Summary*

Certain small methods like lshift8 are called repeatedly but in fact do very little:
These are the internals of lshift8 in an unconstrained context.

if is_unconstrained() {
        if item == 0 {
            0
        } else {
            // Brillig wouldn't shift 0<<4 without overflow.
            item << (8 * shifts)
        }
    }

We can avoid the function call overhead for this method that is itself only a few instructions and is likely to be simplified further as shifts is often a constant.

Additional Context

PR Checklist*

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt on default settings.