Fix hidden env vars not being hidden in closures (#8055)

# Description

This one fixes env not being hidden inside closure, reported in the
conversation under https://github.com/nushell/nushell/issues/6593

https://github.com/nushell/nushell/issues/6593
https://github.com/nushell/nushell/issues/7937 still persist. These
seems a bit more involved and might need hidden env tracking also in the
engine state... I'm not yet sure what's causing it.

Also re-enables some env-related tests and removes unused Value clone.

# User-Facing Changes

Just a bugfix

# Tests + Formatting

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
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass

# After Submitting

If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.

crates/nu-command/src/core_commands/hide_env.rs

@@ -45,7 +45,7 @@ impl Command for HideEnv {
         let ignore_errors = call.has_flag("ignore-errors");
 
         for name in env_var_names {
-            if stack.remove_env_var(engine_state, &name.item).is_none() && !ignore_errors {
+            if !stack.remove_env_var(engine_state, &name.item) && !ignore_errors {
                 let all_names: Vec<String> = stack
                     .get_env_var_names(engine_state)
                     .iter()