Mojo Miji for Mojo v0.26.1

Update Miji for Mojo v0.26.1 (#15)

This PR updates the Miji to be compatible with Mojo v0.26.1, reflecting
API changes and improvements in the new version.

**Changes:**
- Updated all code examples and descriptions to use Mojo v0.26.1 APIs:
`origin_of()` (renamed from `__origin_of()`), `comptime` (replacing
`alias`), `DType.int` (replacing `DType.index`), and the new list
literal/constructor syntax
- Renamed all references to the "DeciMojo" library to "Decimo"
throughout the documentation
- Updated behavioral descriptions to reflect new Mojo v0.26.1 behavior:
string literals auto-materialize to `String`, `List` can now be printed
directly, and the `Writable`/`Stringable` trait usage in the Triangle
example

Mojo Miji for Mojo v0.25.7

mojo_v0.25.7

Update the ownership chapter