Extract COP restart scheduling from BacktrackSolver and improve default policy

[rasros]

What

• Extract restart scheduling from klause/src/commonMain/kotlin/com/eignex/klause/solver/backtrack/Search.kt into a dedicated solver/backtrack/schedule package with a pluggable policy API.
• Keep Luby and Glucose adaptive as schedule implementations behind that API, selected through BacktrackParams.
• Add a COP-oriented default schedule for LCG optimization so fixed/annotation search is robust without hand-tuning lubyRestartBase.

Why

• On largescheduling/instance-0100-1 with -e fixed --lp off, adaptive restart found no feasible solution at 30s and 180s, while Luby-based runs found feasible solutions within 30s.
• The current restart logic is interleaved with DFS control in Search.kt, which makes COP-specific schedule tuning hard to evolve and test independently.