feat: add ignore flag for ignoring directories

[elliottcrif]

• adds ignore flag to optionally ignore directories from being scanned
• tests coming soon

Resolves #93

[elliottcrif]

Currently, the start function takes a growing list of parameters for various options and flags (e.g., show_apparent_size, disable_delete_confirmation). As we continue to add more options, this signature risks becoming unwieldy and harder to maintain. The challenge became especially apparent when updating the UI tests, which required significant changes due to the expanded parameter list.

To address this, I’ve started a WIP implementation that uses the Opt struct as the last argument in start. This encapsulates all optional parameters into a single structure, aiming to reduce churn when adding or modifying options.

I’d appreciate input on the following:

• Is encapsulating options in a configuration struct like Opt an idiomatic approach in Rust?
• Would a builder pattern provide better flexibility and maintainability for this use case?
• Are there other patterns or techniques in Rust that would align well with the goal of minimizing signature changes?

I’m especially interested in feedback on how this impacts code readability, maintainability, and idiomatic usage in Rust.

[elliottcrif]

I have opted to use an ignore option but wondering if we would prefer to use exclude with shorthand x, I have seen that preference voiced in other issues.

[elliottcrif]

cc @imsnif @pjsier @pm100