Fix dirs removal warning (#14029)

# Description

* Primary purpose is to fix an issue with a missing escaped opening
parenthesis in the warning message when running an old `dirs` alias.
This was creating an error condition from improper interpolation.

Also

* Incorporates #13842 feedback from @kubouch by renaming `std/lib` to
`std/util`
* Removes duplication of code in `export-env`
* Renames submodule exports to `std/<submodule>` rather than
`./<submodule>` - No user-facing change other than `view files` appears
"prettier".
* In #13842, I converted the test cases to use `use std/<module>`
syntax. Previously, the tests were (effectively) using `use std *` (due
to pre-existing bugs, now fixed).

So "before", we only had test coverage on `use std *`, and "after" we
only had test coverage on `use std/<module>`. I've started adding test
cases so that we have coverage on *both* scenarios going forward.

For now, `formats` and `util` have been updated with tests for both
scenarios. I'll continue adding the others in future PRs.

# User-Facing Changes

No user-facing changes - Bug fix, refactor, and test cases only

# Tests + Formatting

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting

Still working on updating the Doc. I ran into the `dirs` issue while
writing it and rabbit-trailed to fix it in this PR.

crates/nu-std/std/mod.nu

@@ -1,24 +1,24 @@
 # std.nu, `used` to load all standard library components
 
 # Top-level commands: ellie, repeat, null-device, and "path add"
-export use lib *
+export use std/util *
 
 # std submodules
-export module ./assert
-export module ./bench
-export module ./dt
-export module ./formats
-export module ./help
-export module ./input
-export module ./iter
-export module ./log
-export module ./math
-export module ./xml
+export module std/assert
+export module std/bench
+export module std/dt
+export module std/formats
+export module std/help
+export module std/input
+export module std/iter
+export module std/log
+export module std/math
+export module std/xml
 
 # Load main dirs command and all subcommands
-export use ./dirs main
-export module ./dirs {
-  export use ./dirs [
+export use std/dirs main
+export module dirs {
+  export use std/dirs [
     add
     drop
     next
@@ -29,11 +29,6 @@ export module ./dirs {
 
 # Workaround for #13403 to load export-env blocks from submodules
 export-env {
-    # log
-    $env.NU_LOG_FORMAT = $env.NU_LOG_FORMAT? | default "%ANSI_START%%DATE%|%LEVEL%|%MSG%%ANSI_STOP%"
-    $env.NU_LOG_DATE_FORMAT = $env.NU_LOG_DATE_FORMAT? | default "%Y-%m-%dT%H:%M:%S%.3f"
-    
-    # dirs
-    $env.DIRS_POSITION = 0
-    $env.DIRS_LIST = [($env.PWD | path expand)]
+    use std/log []
+    use std/dirs []
 }