Tracking: remove unregistered-dep workarounds once PureKLU + SparseColumnPivotedQR are registered; revisit Aqua tmax

WHAT: CI.yml:32-36 develops both deps from git URLs on every matrix entry because neither is in any reachable registry (confirmed) — this and the install-doc workaround are the only things letting the package resolve. The [compat] bounds PureKLU="0.1" / SparseColumnPivotedQR="0.1" (Project.toml:29,33) are not registry-enforced until registration, so a breaking change in csr_qr/csr_refactor!/klu! signatures won't be caught by compat. Separately, test/runtests.jl:55-58 raises the Aqua persistent_tasks budget 6x (10s→60s) to work around precompile-contention flakiness — a band-aid that could also hide a genuine future load slowdown. Note: there is NO [sources] block in Project.toml today (only the CI step and README need cleanup). WHY IT MATTERS: Blocked on external registration; folds several low-priority cleanups into one tracking item. FIX: When registration lands — delete the 'Develop unregistered SciML dependencies' CI step, simplify README install to a normal Pkg.add, confirm/tighten the 0.1 compat bounds (let CompatHelper maintain them), verify a clean resolve from General, and re-test whether the default Aqua tmax passes (lower/remove the 60s budget). EFFORT: S.

Priority: low. Filed from an automated next-steps audit of the QR/lstsq work (see PR #6).

After PureKLU and SparseColumnPivotedQR are registered, inspect CI.yml:32-36, Project.toml:29,33, README, and test/runtests.jl:55-58. Confirm a clean General resolve, remove the unregistered-dependency and install workarounds, review the compat bounds, and verify whether Aqua passes with its default persistent_tasks budget.