Convert tidy to a non-egg Python package

It seems that servo-tidy is only used by webrender in my GitHub
searches. WebRender could simply use `rustfmt` and the tidy on pypi
hasn't been updated since 2018. Converting tidy to a normal Python
package removes the maintenance burden of continually fixing the easy
install configuration.

Fixes #29094.
Fixes #29334.

python/tidy/tests/blocked_package.lock

@@ -0,0 +1,26 @@
+[root]
+name = "servo"
+version = "0.0.1"
+
+[[package]]
+name = "test_blocked"
+version = "0.0.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+    "rand 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "test_exception"
+version = "0.0.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+    "rand 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "test_unneeded_exception"
+version = "0.0.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+]