feat(Containers.Result): add `defaultWith` function

```fsharp
let defaultWith defThunk (result: Result<'T, 'Error>) =
match result with
| Ok x -> x
| Error msg -> defThunk msg
```

Locate the Containers.Result module and read nearby Result helper functions to determine the project’s conventions for naming and tests. Add the requested defaultWith function with the behavior shown in the issue, then run the relevant test suite or existing Result tests to confirm Ok and Error cases.

Written by the indexing model from the issue text.