acsmoe 0.1.0

Initial CRAN release.

• Covariance-aware derived-estimate helpers: acs_sum(), acs_diff(), acs_ratio(), acs_prop(), acs_product(), acs_linear(). With no covariance supplied, results match the zero-covariance ACS approximation formulas used by tidycensus.
• Grouped paired estimate/MOE aggregation via acs_aggregate(), with cov_strategy = "zero" (default) and cov_strategy = "constant" for sensitivity analysis.
• Simulation helpers acs_simulate() and acs_simulate_fn() for derived quantities from estimate/MOE pairs.
• MOE/SE/CI conversion utilities: moe_to_se(), se_to_moe(), moe_ci().
• Reliability diagnostics: acs_cv() and acs_reliability().