Added budget cache and implemented public/private simulations behavior

example.env

src/lib/budgets.ts

src/lib/components/BudgetConnexionModal.svelte

src/lib/components/BudgetSimulationSharingModal.svelte

src/lib/components/ReformsChanges.svelte

src/lib/server/auditors/config.ts

src/lib/server/config.ts

src/lib/simulations.ts

src/routes/+layout.svelte

src/routes/+page.svelte

src/routes/budget/+server.ts

src/routes/simulations_budget/+page.svelte

src/routes/simulations_budget/+server.ts

src/routes/simulations_budget/[simulation]/+page.server.ts

src/routes/simulations_budget/[simulation]/+page.svelte

src/routes/simulations_budget/index/+server.ts

src/routes/simulations_budget/server.old.ts