[test] Consider removing `lazy_static`

[ValuedMammal]

Static references don't run their destructors. This means we can end up leaking resources after running the test suite. This issue is only related to tests and not a bug in the library.

rust-esplora-client/src/lib.rs

Lines 281 to 291 in 9305e41

	lazy_static! {
	static ref BITCOIND: corepc_node::Node = {
	let bitcoind_exe = env::var("BITCOIND_EXE")
	.ok()
	.or_else(|| corepc_node::downloaded_exe_path().ok())
	.expect(
	"you need to provide an env var BITCOIND_EXE or specify a bitcoind version feature",
	);
	let conf = corepc_node::Conf::default();
	corepc_node::Node::with_conf(bitcoind_exe, &conf).unwrap()
	};

To reproduce

1. cargo test -- --test-threads=1
2. ps aux | grep bitcoind

Additional Context

• Static items do not call drop.
• impl Drop for Node

[luisschwab]

Nice catch, I've reproduced this behavior. Concept ACK.