Add gif demo for PyPI, readme-replacements config, bump to 0.1.3

- Add trimmed demo.gif (first 50% of webp, 10MB) for PyPI rendering
- Add [tool.release-pypi] readme-replacements to swap webp->gif at build time
- Fix README to use highjax-rl as PyPI package name
- Bump version to 0.1.3

Author: cool-RR

pyproject.toml

@@ -4,7 +4,7 @@ build-backend = "setuptools.build_meta"
 
 [project]
 name = "highjax-rl"
-version = "0.1.2"
+version = "0.1.3"
 description = "HighJax: A JAX implementation of the HighwayEnv driving environment"
 readme = "README.md"
 license = "MIT"
@@ -66,6 +66,11 @@ highjax_trainer = "highjax_trainer:cli"
 [tool.setuptools.package-data]
 highjax = ["behaviors/*.json"]
 
+[tool.release-pypi]
+readme-replacements = [
+    ["demo.webp", "demo.gif"],
+]
+
 [tool.setuptools.packages.find]
 where = ["."]
 include = ["highjax*"]