address review feedback

Adjust error text and naming to conform with best practices.
Use `map_err()` instead of `or()`. Wrap lower-level errors instead of
ignoring their details.

Also, don't "cheat" by bypassing the `new()` function in tests.

Fix a dangling reference in the try_from_into hints.

info.toml

@@ -532,16 +532,19 @@ path = "exercises/error_handling/errors6.rs"
 mode = "test"
 hint = """
 This exercise uses a completed version of `PositiveNonzeroInteger` from
-the errors4.
+errors4.
 
-Below the TODO line, there is an example of using the `.or()` method
-on a `Result` to transform one type of error into another. Try using
-something similar on the `Result` from `parse()`. You might use the `?`
-operator to return early from the function, or you might use a `match`
-expression, or maybe there's another way!
+Below the line that TODO asks you to change, there is an example of using
+the `map_err()` method on a `Result` to transform one type of error into
+another. Try using something similar on the `Result` from `parse()`. You
+might use the `?` operator to return early from the function, or you might
+use a `match` expression, or maybe there's another way!
 
-Read more about `.or()` in the `std::result` documentation:
-https://doc.rust-lang.org/std/result/enum.Result.html#method.or"""
+You can create another function inside `impl ParsePosNonzeroError` to use
+with `map_err()`.
+
+Read more about `map_err()` in the `std::result` documentation:
+https://doc.rust-lang.org/std/result/enum.Result.html#method.map_err"""
 
 # Generics
 
@@ -927,7 +930,7 @@ hint = """
 Follow the steps provided right before the `TryFrom` implementation.
 You can also use the example at https://doc.rust-lang.org/std/convert/trait.TryFrom.html
 
-You might want to look back at the exercise errorsn (or its hints) to remind
+You might want to look back at the exercise errors5 (or its hints) to remind
 yourself about how `Box<dyn Error>` works.
 
 If you're trying to return a string as an error, note that neither `str`