Periodically wake DriverSelect so we can poll whether or not stop had been called.

[maciejhirsz]

Fixes #549. This is all pretty esoteric, but TL;DR is:

• The loop in the per-connection background task has been reworked to more closely resemble the loop in accepting incoming connections, making sure we check the StopMonitor every time the driver has been polled.
• Added an Interval internally in FutureDriver, which is only polled in the DriverSelect instances. It effectively triggers a forced poll every second, which checks the stop flag, which will shut down all loops.

The tests are now properly terminating without having to drop the client (with a 1s delay):

$ cargo test --test resource_limiting
   Compiling jsonrpsee-integration-tests v0.4.1 (/home/maciej/rust/jsonrpsee/tests)
    Finished test [unoptimized + debuginfo] target(s) in 2.94s
     Running tests/resource_limiting.rs (target/debug/deps/resource_limiting-17aaec4a6e8ab5eb)

running 4 tests
test http_server_with_macro_module ... ok
test http_server_with_manual_module ... ok
test ws_server_with_manual_module ... ok
test ws_server_with_macro_module ... ok

test result: ok. 4 passed; 0 failed; 0 ignored; 0 measured; 0 filtered out; finished in 1.00s

[niklasad1]

LGTM,

Did you run benches by any chance?

[dvdplm]

TIL