Revert premature PowerIO dependency merge

[cameronkhanpour]

Summary

Reverts the premature merge of #57. The PowerIO dependency PR was intended to wait for JuliaRegistries/General#157692, but GitHub merged it immediately because the repository does not have required branch checks gating auto-merge.

Validation

This restores Project.toml to the pre-#57 dependency metadata.

[github-actions]

Benchmark Results (Julia v1)

Time benchmarks

	main	0c56a84...	main / 0c56a84...
ac_opf/kkt_jacobian/case30.m	3.46 ± 0.07 ms	3.55 ± 0.081 ms	0.976 ± 0.03
ac_opf/kkt_param/case30.m/switching	0.106 ± 0.0081 ms	0.107 ± 0.0081 ms	0.99 ± 0.11
dc_opf/kkt_jacobian/case30.m/cost_linear	0.16 ± 0.001 μs	0.16 ± 0.01 μs	1 ± 0.063
dc_opf/kkt_jacobian/case30.m/cost_quadratic	0.141 ± 0.011 μs	0.141 ± 0.01 μs	1 ± 0.11
dc_opf/kkt_jacobian/case30.m/demand	0.29 ± 0.04 μs	0.27 ± 0.029 μs	1.07 ± 0.19
dc_opf/kkt_jacobian/case30.m/flowlimit	0.381 ± 0.041 μs	0.38 ± 0.03 μs	1 ± 0.13
dc_opf/kkt_jacobian/case30.m/full	17.9 ± 17 μs	13.2 ± 6.9 μs	1.35 ± 1.4
dc_opf/kkt_jacobian/case30.m/susceptance	0.0866 ± 0.0038 ms	0.0877 ± 0.0038 ms	0.987 ± 0.061
time_to_load	1.71 ± 0.013 s	1.72 ± 0.02 s	0.996 ± 0.014

Memory benchmarks

	main	0c56a84...	main / 0c56a84...
ac_opf/kkt_jacobian/case30.m	0.0339 M allocs: 1.18 MB	0.0339 M allocs: 1.18 MB	1
ac_opf/kkt_param/case30.m/switching	1.49 k allocs: 0.602 MB	1.49 k allocs: 0.602 MB	1
dc_opf/kkt_jacobian/case30.m/cost_linear	6 allocs: 0.328 kB	6 allocs: 0.328 kB	1
dc_opf/kkt_jacobian/case30.m/cost_quadratic	6 allocs: 0.328 kB	6 allocs: 0.328 kB	1
dc_opf/kkt_jacobian/case30.m/demand	6 allocs: 1.42 kB	6 allocs: 1.42 kB	1
dc_opf/kkt_jacobian/case30.m/flowlimit	6 allocs: 1.89 kB	6 allocs: 1.89 kB	1
dc_opf/kkt_jacobian/case30.m/full	0.079 k allocs: 0.082 MB	0.079 k allocs: 0.082 MB	1
dc_opf/kkt_jacobian/case30.m/susceptance	2.28 k allocs: 0.292 MB	2.28 k allocs: 0.292 MB	1
time_to_load	0.149 k allocs: 11.1 kB	0.149 k allocs: 11.1 kB	1