Fix decorator ranges

Incorrectly merged LALRPOP file

Remove Range type parameter from AST nodes (#15)

Fix range of keyword identifier (#14)

Fix ArgWithDefault TextRange (#13)

Add `TextRange` to `Identifier` (#8)

## Summary

This PR adds `TextRange` to `Identifier`. Right now, the AST only
includes ranges for identifiers in certain cases (`Expr::Name`,
`Keyword`, etc.), namely when the identifier comprises an entire AST
node. In Ruff, we do additional ad-hoc lexing to extract identifiers
from source code.

One frequent example: given a function `def f(): ...`, we lex to find
the range of `f`, for use in diagnostics.

Another: `except ValueError as e`, for which the AST doesn't include a
range for `e`.

Note that, as an optimization, we avoid storing the `TextRange` for
`Expr::Name`, since it's already included.

Make malachite-bigint an optional dependency for rustpython-format (#12)

Add `Decorator` node (#7)