Fix hidden env vars not being hidden in closures

[kubouch]

Description

This one fixes env not being hidden inside closure, reported in the conversation under #6593

#6593 #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 after the PR is merged, if necessary. This will help us keep the docs up to date.

[codecov]

Codecov Report

Base: 55.24% // Head: 55.71% // Increases project coverage by +0.47% 🎉

Coverage data is based on head (b50b064) compared to base (2894668).
Patch coverage: 88.88% of modified lines in pull request are covered.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8055      +/-   ##
==========================================
+ Coverage   55.24%   55.71%   +0.47%     
==========================================
  Files         606      604       -2     
  Lines       99060    97500    -1560     
==========================================
- Hits        54721    54324     -397     
+ Misses      44339    43176    -1163     

Impacted Files	Coverage Δ
crates/nu-protocol/src/engine/stack.rs	75.83% <87.50%> (ø)
crates/nu-command/src/core_commands/hide_env.rs	90.90% <100.00%> (ø)
crates/nu-utils/src/utils.rs	45.33% <0.00%> (-9.34%)	⬇️
crates/nu-path/src/helpers.rs	75.00% <0.00%> (-9.22%)	⬇️
crates/nu-utils/src/locale.rs	95.00% <0.00%> (-5.00%)	⬇️
crates/nu-command/src/path/expand.rs	79.59% <0.00%> (-4.02%)	⬇️
crates/nu-engine/src/env.rs	51.96% <0.00%> (-2.51%)	⬇️
crates/nu-command/src/path/join.rs	76.71% <0.00%> (-2.14%)	⬇️
crates/nu-command/src/filesystem/cd_query.rs	52.36% <0.00%> (-1.98%)	⬇️
crates/nu-command/src/path/exists.rs	89.18% <0.00%> (-1.72%)	⬇️
... and 26 more

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