Add justfile and nightly config

In preparation for using a pinned nightly in CI add a `nightly-version`
file and also a `justfile` that uses it.

justfile

@@ -0,0 +1,38 @@
+default:
+  @just --list
+
+# Cargo build everything.
+build:
+  cargo build --workspace --all-targets --all-features
+
+# Cargo check everything.
+check:
+  cargo check --workspace --all-targets --all-features
+
+# Lint everything.
+lint:
+  cargo +$(cat ./nightly-version) clippy --workspace --all-targets --all-features -- --deny warnings
+
+# Run cargo fmt
+fmt:
+  cargo +$(cat ./nightly-version) fmt --all
+
+# Check the formatting
+format:
+  cargo +$(cat ./nightly-version) fmt --all --check
+
+# Quick and dirty CI useful for pre-push checks.
+sane: lint
+  cargo test --quiet --workspace --all-targets --no-default-features > /dev/null || exit 1
+  cargo test --quiet --workspace --all-targets > /dev/null || exit 1
+  cargo test --quiet --workspace --all-targets --all-features > /dev/null || exit 1
+
+  # doctests don't get run from workspace root with `cargo test`.
+  cargo test --quiet --workspace --doc || exit 1
+
+  # Make an attempt to catch feature gate problems in doctests
+  cargo test --manifest-path bitcoin/Cargo.toml --doc --no-default-features > /dev/null || exit 1
+
+# Update the recent and minimal lock files.
+update-lock-files:
+  contrib/update-lock-files.sh

nightly-version

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+nightly-2024-05-04