Reorganize rust crates into a flat crates directory, simplify some CI steps (#4496)

* Move all rust crates (except lib) into crates dir, w/o nesting

* Remove stale path from .gitattributes

* Rename lib.rs files for easier navigation

* Rename mod.rs file for easier navigation

* Fix emscripten-version path

* Fix fixtures dir paths

* Use the default rustfmt settings

* Don't use nightly on CI

cli/src/templates/gitattributes

@@ -1,41 +0,0 @@
-* text=auto eol=lf
-
-# Generated source files
-src/*.json linguist-generated
-src/parser.c linguist-generated
-src/tree_sitter/* linguist-generated
-
-# C bindings
-bindings/c/** linguist-generated
-CMakeLists.txt linguist-generated
-Makefile linguist-generated
-
-# Rust bindings
-bindings/rust/* linguist-generated
-Cargo.toml linguist-generated
-Cargo.lock linguist-generated
-
-# Node.js bindings
-bindings/node/* linguist-generated
-binding.gyp linguist-generated
-package.json linguist-generated
-package-lock.json linguist-generated
-
-# Python bindings
-bindings/python/** linguist-generated
-setup.py linguist-generated
-pyproject.toml linguist-generated
-
-# Go bindings
-bindings/go/* linguist-generated
-go.mod linguist-generated
-go.sum linguist-generated
-
-# Swift bindings
-bindings/swift/** linguist-generated
-Package.swift linguist-generated
-Package.resolved linguist-generated
-
-# Zig bindings
-build.zig linguist-generated
-build.zig.zon linguist-generated