* Replace direct `fmt.Println()` usage in a test with `t.Log()`
* Rename `cmd` to `cli`
* Move asdf command from module root
* Fix some linter warnings, thus enabling some tests that were being skipped
* Fix `Makefile`
* Rename module to `github.com/asdf-vm/asdf`
* Fix `TestGetAllToolsAndVersionsInContent/returns_empty_list_with_found_true_and_no_error_when_empty_content`
* Rewrite `Unique()` to be a bit more straightforwards
* Get workflow checks passing again
toolversions.Unique is ever so slightly faster, technically.
```
goos: linux
goarch: amd64
pkg: github.com/asdf-vm/asdf/internal/toolversions
cpu: AMD Ryzen 9 3900X 12-Core Processor
│ /tmp/old.txt │ /tmp/new.txt │
│ sec/op │ sec/op vs base │
Unique-24 346.5n ± 1% 342.4n ± 1% -1.17% (p=0.027 n=10)
│ /tmp/old.txt │ /tmp/new.txt │
│ B/op │ B/op vs base │
Unique-24 160.0 ± 0% 160.0 ± 0% ~ (p=1.000 n=10) ¹
¹ all samples are equal
│ /tmp/old.txt │ /tmp/new.txt │
│ allocs/op │ allocs/op vs base │
Unique-24 3.000 ± 0% 3.000 ± 0% ~ (p=1.000 n=10) ¹
¹ all samples are equal
```
* Create `CurrentEnv` and `MergeEnv` helper functions
* Add another test for `paths.RemoveFromPath` function
* Move executable finding functions to shims package
* Correct PATH code for env and exec commands
* Create `CallbackPath` method on `Plugin` struct
* Correct behavior of `asdf shimversions` command
* Update `shims.FindExecutable` function to return plugin
* Create `repotest.WritePluginCallback` function
* Create `execenv` package for invoking `exec-env` plugin callback
* Make `MapToSlice` a public function
* Return resolved version from `shims.FindExecutable` function
* Create `shims.ExecutablePaths` function
* Enable `shim_env_command.bats` tests
* Implement `asdf env` command
