Raise LinearSolve sublibrary floor to 5.4

[ChrisRackauckas-Claude]

Please ignore this PR until it has been reviewed by @ChrisRackauckas.

Follow-up to #1163, which raised the LinearSolve floor to 5.4 in NonlinearSolve and NonlinearSolveBase. The FirstOrder and QuasiNewton sublibraries were left at LinearSolve = "5".

What changed

Pure [compat] lower-bound bump in two independently tested sublibraries:

• lib/NonlinearSolveFirstOrder/Project.toml: LinearSolve = "5" → "5.4"
• lib/NonlinearSolveQuasiNewton/Project.toml: LinearSolve = "5" → "5.4"

No solver code, tests, or package versions were changed.

Why

Downgrade Sublibraries on master is red while the matching parent Downgrade and latest CI (NonlinearSolve) runs are not. The failing jobs are only:

• https://github.com/SciML/NonlinearSolve.jl/actions/runs/31802446977/job/94783357301 (lib/NonlinearSolveQuasiNewton)
• https://github.com/SciML/NonlinearSolve.jl/actions/runs/31802446977/job/94783357377 (lib/NonlinearSolveFirstOrder)

Downgrade pins each sublibrary's declared LinearSolve floor. With "5" that is LinearSolve 5.0.0, which cannot satisfy in-tree NonlinearSolveBase (LinearSolve = "5.4"):

Unsatisfiable requirements detected for package LinearSolve
 ├─restricted to versions 5 by NonlinearSolveQuasiNewton
 ├─restricted to versions 5.4.0-5 by NonlinearSolveBase
 └─restricted to versions 5.0.0 by an explicit requirement

Verification

Julia 1.10.11, Pkg.develop of each sublibrary, then Pkg.add(name="LinearSolve", version=...):

Sublibrary	LinearSolve 5.0.0 (old floor)	LinearSolve 5.4.0 (new floor)
NonlinearSolveFirstOrder	unsatisfiable	resolves
NonlinearSolveQuasiNewton	unsatisfiable	resolves

Not verified here: the full Core/QA/GPU test groups, or whether other sublibraries have similar floors (only these two jobs were red on the latest Downgrade Sublibraries run).

Stale related PR: #1143 (parent-only LinearSolve 5.4 bump; superseded by #1163).

[ChrisRackauckas-Claude]

Independent clean-master validation of the merged floor alignment:

• On 30fd52ec61872225af8cc975e4a1f354ee5cffca, Julia 1.10.11 environments developing the current local NonlinearSolveBase reproduce both resolver failures when explicitly pinned to the sublibrary floor LinearSolve@5.0.0. The parent 4816e1c067fadc3ed4c7ad058c797bff08da2ac3 resolves both at 5.0.0; with this PR's two floor changes, both current-source environments resolve at LinearSolve 5.4.0.
• NonlinearSolveFirstOrder current-graph Core passed, including General NLLS 480/480, NewtonRaphson 309/309, PseudoTransient 51/51, TrustRegion 1176/1176, LevenbergMarquardt 33/33, sparse AutoDiff 12/12, structured Jacobians 16/16, and the final package success. QA passed 20/20 in 2m24.0s.
• NonlinearSolveQuasiNewton current-graph Core passed, including Broyden 594/594, Klement 216/216, LimitedMemoryBroyden 99/99, update-rule reinit 63/63, and the final package success. QA passed 20/20 in 1m56.0s.
• Runic, typos on both changed Project files, and git diff --check all exited 0. A docs build is not applicable to this compat-only change.

The exact assigned clean-master failures were:

• FirstOrder: https://github.com/SciML/NonlinearSolve.jl/actions/runs/31802132870/job/94772724474
• QuasiNewton: https://github.com/SciML/NonlinearSolve.jl/actions/runs/31802132870/job/94772724439