fix!: prevent inconsistent language usage in Driver

[TomAFrench]

Related issue(s)

Resolves #880

Description

Summary of changes

I've removed np_language from the interface of Driver and it now just uses the locally stored language when compiling.

We could make this a non-breaking change by maintaining the same interface while adding an assert_eq(np_language, &self.langauge) to each method which uses it. My feeling however is that we're going to be the only consumer of this API currently so we can make this breaking change safely.

Dependency additions / changes

Test additions / changes

Checklist

• I have tested the changes locally.
• I have formatted the changes with Prettier and/or cargo fmt with default settings.
• I have linked this PR to the issue(s) that it resolves.
• I have reviewed the changes on GitHub, line by line.
• I have ensured all changes are covered in the description.
• This PR requires documentation updates when merged.

Additional context