Consolidate dependency files (environment.yml vs requirements.txt vs requirements-build.txt)

[mmcky]

Summary

There are three overlapping dependency manifests that disagree on the details, and only one of them is actually used. This makes it easy for deps to rot and — more importantly — means a local setup that follows the README can't run the JAX lectures.

The three files

File	Contents	Used by?
environment.yml	python=3.13 + anaconda metapackage + pip: jupyter-book & sphinx stack	✅ the only one CI uses (environment-file: environment.yml)
requirements.txt	matplotlib, numpy, jax, numba	❌ referenced nowhere
requirements-build.txt	matplotlib, numpy, jax, numba + jupyter-book & sphinx stack	❌ referenced nowhere

grep confirms nothing in .github/, scripts/, or README.md references either requirements*.txt. CI builds the env from environment.yml, then installs JAX out of band via pip install -U jax (ci.yml, publish.yml).

Problems

1. No single source of truth — three files, two of them orphaned and liable to rot.
2. Redundancy via the anaconda metapackage — anaconda already bundles numpy, matplotlib, and numba, so the explicit lines in the requirements files duplicate it.
3. numba is listed everywhere but unused (via anaconda + both requirements files) — see Numba is advertised but never used (no Numba lecture/code) #2 (Numba advertised but unused).
4. Likely channel typo — environment.yml declares channels: - default (singular); the canonical conda channel is defaults, which the other QuantEcon lecture repos use.

Suggested direction

Pick one source of truth. Two QuantEcon-friendly shapes:

• Conda-first (matches CI): add jax to environment.yml, drop the unused numba, fix defaults, and delete both requirements*.txt. The separate CI pip install -U jax could then go away.
• Keep a minimal requirements.txt for the Colab / "just run the notebooks" path (matplotlib, numpy, jax), referenced from notebooks/README.md, and make environment.yml the single build source of truth (remove requirements-build.txt).

Either way: one runtime manifest + at most one build manifest, JAX listed where the README points, and the channel name corrected.

Open question before any consolidation

Related: #2 (numba unused), #5 (GPU runner / RunsOn).

[Smit-create]

Hey @mmcky,

1. I have kept environment.yml so that the attendees of the workshop can just use this file to create a new environment on their local machine if they already have Anaconda installed on their machines.
2. I also kept requirements.txt for the attendees who don't use Anaconda and want to just pip install to run these lectures.
3. requirements-build.txt can be removed as it was used by me to build and test the lectures locally. I will remove this.