Add explicit binding

I thought I already filed this, but I cannot find it. Sorry if it's a reiterated request.

The problem we have with box is that the imported symbols are not explicitly bound. This angers linters, that see a symbol appear out of thin air and start complaining.

Example

```
box::use(mod/hello_world)

hello_world$hello('Ross')
```

This would trigger a linter problem because hello_world appears from nowhere.

I propose to support the additional syntax

```
hello_world <- box::use("mod/hello_world")

hello_world$hello('Ross')
```

This has the added benefit of allowing for easy renaming of the module in case of collision.

The issue names the box::use import syntax and shows the proposed explicit binding and module renaming forms, but it does not identify implementation files or tests. Start by locating the parser and import-binding handling for box::use, then determine how syntax errors and name collisions are tested. Done means explicit bindings work without linter complaints while existing import syntax remains supported.

Written by the indexing model from the issue text.