Document DEQs public alias

[ChrisRackauckas-Claude]

Summary

This PR completes the public API documentation audit for the exported DEQs module alias. It adds a source docstring at the alias definition and keeps the rendered API-page coverage for the alias.

Documenter currently canonicalizes module-valued alias doc objects to the aliased module during missing_docs, so @docs DeepEquilibriumNetworks.DEQs cannot satisfy the DeepEquilibriumNetworks.DEQs binding. The docs build now drops that single alias binding from Documenter metadata and relies on the existing API prose for rendered docs coverage.

Ignore this PR until it has been reviewed by @ChrisRackauckas.

Validation

• git diff --check
• Runic.jl 1.7.0 check on src/DeepEquilibriumNetworks.jl and docs/make.jl
• Julia exported-docstring audit for explicit exported names: DEQs, DeepEquilibriumNetwork, DeepEquilibriumSolution, MultiScaleDeepEquilibriumNetwork, MultiScaleNeuralODE, MultiScaleSkipDeepEquilibriumNetwork, SkipDeepEquilibriumNetwork; result: no undocumented exports
• julia +1.10 --project=docs -e 'using Pkg; Pkg.instantiate(); include("docs/make.jl")' passed locally. It emitted existing warnings for arXiv HTTP redirects, a large generated tutorial page, and skipped deployment outside CI.\n- Pkg.test() was attempted and fails before layer assertions because OrdinaryDiffEq fails to precompile: OrdinaryDiffEqBDF cannot import OrdinaryDiffEqCore.find_algebraic_vars_eqs. The same failure reproduces on clean origin/main at ad4f946, so it is pre-existing and tracked in Pkg.test fails to precompile OrdinaryDiffEq on main #224.