refactor: split main.rs into separate modules and library crate

[nightlark]

Adds some organization using modules instead of everything being in main.rs to prepare for future development, and moves most of the logic to a library crate that gets used by the main dapper binary so that people could potentially use dapper as a dependency in other projects.

[Copilot]

Copilot reviewed 6 out of 7 changed files in this pull request and generated 1 comment.

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• src/walker.rs: Evaluated as low risk

Copilot reviewed 6 out of 7 changed files in this pull request and generated no comments.

Files not reviewed (1)

• src/main.rs: Evaluated as low risk

Comments suppressed due to low confidence (1)

src/parser.rs:54

• [nitpick] The error message could be more informative by including the node information. Suggested change: eprintln!("Error reading include name as utf8 text from {} at node {:?}: {}", file_path, node, e);

eprintln!("Error reading include name as utf8 text from {}: {}", file_path, e);