Refactor nu-check (#12137)

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# Description
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This PR refactors `nu-check` and makes it possible to check module
directories. Also removes the requirement for files to end with .nu: It
was too limiting for module directories and there are executable scripts
[around](https://github.com/nushell/nu_scripts/tree/main/make_release/release-note)
that do not end with .nu, it's a common practice for scripts to omit it.

Other changes are:
* Removed the `--all` flag and heuristic parse because these are
irrelevant now when module syntax is a subset of script syntax (i.e.,
every module can be parsed as script).
* Reduced code duplication and in general tidied up the code
* Replaced unspanned errors with spanned ones.

# User-Facing Changes
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helps us keep track of breaking changes. -->

* `nu-check` doesn't require files to end with .nu
* can check module directories
* Removed `--all` flag 

# Tests + Formatting
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Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

- `cargo fmt --all -- --check` to check standard code formatting (`cargo
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- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used` to
check that you're using the standard code style
- `cargo test --workspace` to check that all tests pass (on Windows make
sure to [enable developer
mode](https://learn.microsoft.com/en-us/windows/apps/get-started/developer-mode-features-and-debugging))
- `cargo run -- -c "use std testing; testing run-tests --path
crates/nu-std"` to run the tests for the standard library

> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```
-->

# After Submitting
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