feat(emmylua_check): library

[mrcjkb]

This PR introduces a cli feature flag (enabled by default) to emmylua_check.
If disabled, it removes the clap dependency. This should allow the use of emmylua_check as a library in CLI applications that use a conflicting version of clap (see #580).

If you agree with this approach, I'll look into implementing the same for the other CLI tools.

[CppCXY]

Please fix test

[mrcjkb]

🤔 hmm, this test failure seems unrelated. Is it passing on main?
Edit: It also fails here on main.

failures:

---- handlers::test::hover_function_test::tests::test_3 stdout ----

thread 'handlers::test::hover_function_test::tests::test_3' panicked at crates/emmylua_ls/src/handlers/test/hover_function_test.rs:117:9:
assertion failed: ws.check_hover(r#"
                ---@type Hover.Test3<string>
                local test3

                local <??>event = test3.event
            "#,
    VirtualHoverResult {
        value: "```lua\n(method) Test3:event(event: \"B\", key: string)\n```\n\n&nbsp;&nbsp;in class `Hover.Test3`\n\n---\n\n---\n\n```lua\n(method) Test3:event(event: \"A\", key: string)\n```".to_string(),
    })