Tie electrsd into CI

During import of `electrsd` I just clobbered all CI. Add `electrsd` to
the CI infrastructure in this repo. Use `extra_tests.sh` to mirror the
behaviour in the original repo _excluding_ the no-download test.
Skipping the no-download test because I'm too lazy to set it up, we
don't test no-download in `corepc-node` either.

Author: tcharding

electrsd/contrib/extra_tests.sh

@@ -0,0 +1,45 @@
+#!/usr/bin/env bash
+#
+# Additional tests for `electrs`.
+#
+# This script was written based on CI in
+# `github.com/RCasatta/electrsd` when the crate was imported to this repo.
+# (HEAD on that repo was: dc88d81520c9ec507fc830b88a3b92a034dbaf93).
+
+set -euox pipefail
+
+# Use the current `Cargo.lock` file without updating it.
+cargo="cargo --locked"
+
+
+main() {
+    corepc_node_versions
+    electrs_versions
+    electrs_esplora
+}
+
+corepc_node_versions() {
+    local corepc_node_versions=("corepc-node_29_0" "corepc-node_28_2" "corepc-node_27_2" "corepc-node_26_2" "corepc-node_25_2")
+
+    for feature in "${corepc_node_versions}"; do
+        $cargo test --features="$feature,electrs_0_10_6"
+    done
+}
+
+electrs_versions() {
+    local electrs_versions=("electrs_0_10_6" "electrs_0_9_11" "electrs_0_9_1" "electrs_0_8_10")
+
+    for feature in "${electrs_versions}"; do
+        $cargo test --features="corepc-node_29_0,$feature"
+    done
+}
+
+electrs_esplora() {
+    $cargo test --features="corepc-node_22_1,legacy,esplora_a33e97e1"
+}
+
+#
+# Main script
+#
+main "$@"
+exit 0

electrsd/contrib/test_vars.sh

@@ -0,0 +1,18 @@
+# No shebang, this file should not be executed.
+# shellcheck disable=SC2148
+#
+# disable verify unused vars, despite the fact that they are used when sourced
+# shellcheck disable=SC2034
+
+# Test all these features with "std" enabled.
+FEATURES_WITH_STD=""
+
+# Test all these features without "std" or "alloc" enabled.
+FEATURES_WITHOUT_STD=""
+
+# Run these examples.
+EXAMPLES=""
+
+# Just check the latest minor version of the last three supported Core versions.
+# This is mainly for docs and MSRV - integration tests will catch any other errors.
+EXACT_FEATURES=("download,28_2" "download,27_2" "download,26_2")