Model historical fee inclusion confidence

[rearden-grok]

Summary

• Replace block package-p10 history with vsize-weighted transaction fee hurdles and empirical inclusion curves over actual-height rolling windows.
• Backfill recent txstat rows up to a 1 GiB byte budget, keep the in-memory history bounded by that budget, and update it incrementally on connects and reorgs.
• Keep the 1-block estimate primarily flow-driven at 99.9% confidence; blend live and historical probabilities for 2+ block targets at 99% empirical confidence.
• Report useful preload progress and completion statistics without per-height warning noise; document the model and add an unreleased changelog entry.

Verification

• cargo fmt --all -- --check
• cargo test -p rbitcoin-mempool --lib --quiet
• cargo test -p rbitcoin-query --lib --quiet
• Targeted rbitcoin-net fee history storage and far-horizon tests
• cargo check -p rbitcoin-node --lib --quiet
• Clippy with -D warnings for the four affected crates (--lib)

The local AST scan could not run because ast-grep is not installed in the VM. Required CI will run it.