Reversion operator (~) is not defined for Symbolic Coefficients when using Grassmann and Reduce

I was following along with the examples presented in [Symbolic Coefficients by Declairing Albegra](https://grassmann.crucialflow.com/stable/algebra/#Symbolic-coefficients-by-declaring-algebra), and all was working as expected, until I tried to rotate a point `P` using the symbolically defined `R`, as in the equation `Q = R*P*~R`.

At this point, an error was thrown, indicating

```
ERROR: MethodError: no method matching grade(::Expr)
Closest candidates are:
grade(::Any, ::SubManifold{V, G, B} where G) where {V, B} at ~/.julia/packages/DirectSum/XQ4T8/src/generic.jl:139
```

Start with the linked “Symbolic Coefficients by Declaring Algebra” example and reproduce the expression Q = R*P*~R using Grassmann and Reduce. Investigate the reported grade(::Expr) MethodError during reversion. Done means symbolic coefficients support the reversion operator in this example without the reported error.

Written by the indexing model from the issue text.