Simplify GPU admonition and add to all JAX lectures

[mmcky]

Summary

This PR simplifies the GPU admonition text and ensures all JAX lectures include the GPU notice.

Changes

1. Simplified GPU Admonition

Updated lectures/_admonition/gpu.md from:

This lecture was built using a machine with the latest CUDA and CUDANN frameworks 
installed with access to a GPU.

To run this lecture on Google Colab, click on the "play" icon top right, select 
Colab, and set the runtime environment to include a GPU.

To run this lecture on your own machine, you need to install the software listed 
following this notice.

To:

This lecture is designed to run on a GPU. To use Google Colab's free GPUs, 
click the play icon top right, select Colab, and set the runtime to include a GPU.

For local GPU setup, see the JAX installation guide.

2. Added GPU Admonition to 17 JAX Lectures

The following lectures were missing the GPU admonition and now include it:

• aiyagari.md
• ak_aiyagari.md
• endogenous_lake.md
• ifp_advanced.md
• ifp_discrete.md
• ifp_egm.md
• ifp_egm_transient_shocks.md
• ifp_opi.md
• lake_model.md
• mccall_fitted_vfi.md
• mccall_model.md
• mccall_model_with_sep_markov.md
• mccall_model_with_separation.md
• mccall_persist_trans.md
• mle.md
• newton_method.md
• os_egm_jax.md

Benefits

• More concise, user-friendly GPU notice
• Consistent with lecture-jax (PR ENH: Add link checker GitHub Action #258) and lecture-python-programming.myst (PR Execution issue Github Actions Environment #447)
• All 21 JAX lectures now have proper GPU admonitions
• Single source of truth via _admonition/gpu.md

[github-actions]

📖 Netlify Preview Ready!

Preview URL: https://pr-751--sunny-cactus-210e3e.netlify.app (39b96d3)

📚 Changed Lecture Pages: aiyagari, ak_aiyagari, endogenous_lake, ifp_advanced, ifp_discrete, ifp_egm, ifp_egm_transient_shocks, ifp_opi, lake_model, mccall_fitted_vfi, mccall_model, mccall_model_with_sep_markov, mccall_model_with_separation, mccall_persist_trans, mle, newton_method, os_egm_jax

[github-actions]

📖 Netlify Preview Ready!

Preview URL: https://pr-751--sunny-cactus-210e3e.netlify.app (8320250)

📚 Changed Lecture Pages: aiyagari, ak_aiyagari, endogenous_lake, ifp_advanced, ifp_discrete, ifp_egm, ifp_egm_transient_shocks, ifp_opi, lake_model, mccall_fitted_vfi, mccall_model, mccall_model_with_sep_markov, mccall_model_with_separation, mccall_persist_trans, mle, newton_method, os_egm_jax