nu-cli refactor moving commands into their own crate nu-command (#2910)

* move commands, futures.rs, script.rs, utils

* move over maybe_print_errors

* add nu_command crate references to nu_cli

* in commands.rs open up to pub mod from pub(crate)

* nu-cli, nu-command, and nu tests are now passing

* cargo fmt

* clean up nu-cli/src/prelude.rs

* code cleanup

* for some reason lex.rs was not formatted, may be causing my error

* remove mod completion from lib.rs which was not being used along with quickcheck macros

* add in allow unused imports

* comment out one failing external test; comment out one failing internal test

* revert commenting out failing tests; something else might be going on; someone with a windows machine should check and see what is going on with these failing windows tests

* Update Cargo.toml

Extend the optional features to nu-command

Co-authored-by: Jonathan Turner <jonathandturner@users.noreply.github.com>

crates/nu-command/tests/format_conversions/eml.rs

@@ -0,0 +1,93 @@
+use nu_test_support::{nu, pipeline};
+
+const TEST_CWD: &str = "tests/fixtures/formats";
+
+// The To field in this email is just "to@example.com", which gets parsed out as the Address. The Name is empty.
+#[test]
+fn from_eml_get_to_field() {
+    let actual = nu!(
+        cwd: TEST_CWD,
+        pipeline(
+            r#"
+            open sample.eml
+            | get To
+            | get Address
+        "#
+        )
+    );
+
+    assert_eq!(actual.out, "to@example.com");
+
+    let actual = nu!(
+        cwd: TEST_CWD,
+        pipeline(
+            r#"
+            open sample.eml
+            | get To
+            | get Name
+        "#
+        )
+    );
+
+    assert_eq!(actual.out, "");
+}
+
+// The Reply-To field in this email is "replyto@example.com" <replyto@example.com>, meaning both the Name and Address values are identical.
+#[test]
+fn from_eml_get_replyto_field() {
+    let actual = nu!(
+        cwd: TEST_CWD,
+        pipeline(
+            r#"
+            open sample.eml
+            | get Reply-To
+            | get Address
+        "#
+        )
+    );
+
+    assert_eq!(actual.out, "replyto@example.com");
+
+    let actual = nu!(
+        cwd: TEST_CWD,
+        pipeline(
+            r#"
+            open sample.eml
+            | get Reply-To
+            | get Name
+        "#
+        )
+    );
+
+    assert_eq!(actual.out, "replyto@example.com");
+}
+
+#[test]
+fn from_eml_get_subject_field() {
+    let actual = nu!(
+        cwd: TEST_CWD,
+        pipeline(
+            r#"
+            open sample.eml
+            | get Subject
+        "#
+        )
+    );
+
+    assert_eq!(actual.out, "Test Message");
+}
+
+#[test]
+fn from_eml_get_another_header_field() {
+    let actual = nu!(
+        cwd: TEST_CWD,
+        pipeline(
+            r#"
+            open sample.eml
+            | get MIME-Version
+        "#
+        )
+    );
+
+    assert_eq!(actual.out, "1.0");
+}