Will panic on new rust due to use of outdated actix -> smallvec dependency

Hi! In rust-lang/rust#99389 we're making the checks for uninitialized memory stricter, and this crate runs into those. Here's the panics that are ran into.

     Running tests/test_topology.rs (/home/jess/.cache/cargo/target/debug/deps/test_topology-d3bc9af299f168dc)

running 1 test
 ERROR tempest::metric > Error reading aggregate metrics file: "/tmp/aggregate-metrics-agent" Os { code: 2, kind: NotFound, message: "No such file or directory" }
test simple ... FAILED

failures:

---- simple stdout ----
thread '<unnamed>' panicked at 'attempted to leave type `[actix::contextitems::ActorWaitItem<service::agent::AgentService>; 2]` uninitialized, which is invalid', /home/jess/.cargo/registry/src/github.com-1ecc6299db9ec823/smallvec-0.6.10/lib.rs:410:49
stack backtrace:
   0: rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::panic
   3: core::mem::uninitialized
             at /home/jess/src/rust/library/core/src/mem/mod.rs:685:9
   4: smallvec::SmallVec<A>::new
             at /home/jess/.cargo/registry/src/github.com-1ecc6299db9ec823/smallvec-0.6.10/lib.rs:410:49
   5: actix::contextimpl::ContextParts<A>::new
             at /home/jess/.cargo/registry/src/github.com-1ecc6299db9ec823/actix-0.8.3/src/contextimpl.rs:72:19
   6: actix::context::Context<A>::new
             at /home/jess/.cargo/registry/src/github.com-1ecc6299db9ec823/actix-0.8.3/src/context.rs:89:20
   7: actix::actor::Actor::create
             at /home/jess/.cargo/registry/src/github.com-1ecc6299db9ec823/actix-0.8.3/src/actor.rs:193:23
   8: tempest::service::agent::AgentService::run
             at ./src/service/agent.rs:61:9
   9: tempest::rt::test::run::{{closure}}
             at ./src/rt.rs:225:13
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
thread '<unnamed>' panicked at 'attempted to leave type `[actix::contextitems::ActorWaitItem<service::agent_client::AgentClient>; 2]` uninitialized, which is invalid', /home/jess/.cargo/registry/src/github.com-1ecc6299db9ec823/smallvec-0.6.10/lib.rs:410:49
stack backtrace:
   0: rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::panic
   3: core::mem::uninitialized
             at /home/jess/src/rust/library/core/src/mem/mod.rs:685:9
   4: smallvec::SmallVec<A>::new
             at /home/jess/.cargo/registry/src/github.com-1ecc6299db9ec823/smallvec-0.6.10/lib.rs:410:49
   5: actix::contextimpl::ContextParts<A>::new
             at /home/jess/.cargo/registry/src/github.com-1ecc6299db9ec823/actix-0.8.3/src/contextimpl.rs:72:19
   6: actix::context::Context<A>::new
             at /home/jess/.cargo/registry/src/github.com-1ecc6299db9ec823/actix-0.8.3/src/context.rs:89:20
   7: actix::actor::Actor::start
             at /home/jess/.cargo/registry/src/github.com-1ecc6299db9ec823/actix-0.8.3/src/actor.rs:128:9
   8: tempest::service::agent_client::AgentClient::connect
             at ./src/service/agent_client.rs:53:27
   9: tempest::metric::backend::MetricsAggregateActor::new
             at ./src/metric/backend/mod.rs:347:27
  10: tempest::service::topology::TopologyService::run
             at ./src/service/topology.rs:156:37
  11: tempest::rt::test::run::{{closure}}
             at ./src/rt.rs:231:13
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
thread '<unnamed>' panicked at 'attempted to leave type `[actix::contextitems::ActorWaitItem<service::agent_client::AgentClient>; 2]` uninitialized, which is invalid', /home/jess/.cargo/registry/src/github.com-1ecc6299db9ec823/smallvec-0.6.10/lib.rs:410:49
stack backtrace:
   0: rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::panic
   3: core::mem::uninitialized
             at /home/jess/src/rust/library/core/src/mem/mod.rs:685:9
   4: smallvec::SmallVec<A>::new
             at /home/jess/.cargo/registry/src/github.com-1ecc6299db9ec823/smallvec-0.6.10/lib.rs:410:49
   5: actix::contextimpl::ContextParts<A>::new
             at /home/jess/.cargo/registry/src/github.com-1ecc6299db9ec823/actix-0.8.3/src/contextimpl.rs:72:19
   6: actix::context::Context<A>::new
             at /home/jess/.cargo/registry/src/github.com-1ecc6299db9ec823/actix-0.8.3/src/context.rs:89:20
   7: actix::actor::Actor::start
             at /home/jess/.cargo/registry/src/github.com-1ecc6299db9ec823/actix-0.8.3/src/actor.rs:128:9
   8: tempest::service::agent_client::AgentClient::connect
             at ./src/service/agent_client.rs:53:27
   9: tempest::metric::backend::MetricsAggregateActor::new
             at ./src/metric/backend/mod.rs:347:27
  10: tempest::service::task::TaskService::run
             at ./src/service/task.rs:239:37
  11: tempest::rt::task::run
             at ./src/rt.rs:326:9
  12: tempest::rt::test::run::{{closure}}
             at ./src/rt.rs:260:17
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
thread 'simple' panicked at 'assertion failed: `(left == right)`
  left: `None`,
 right: `Some(1000)`', tempest/tests/test_topology.rs:17:5
stack backtrace:
   0: rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::panicking::assert_failed_inner
   3: core::panicking::assert_failed
             at /home/jess/src/rust/library/core/src/panicking.rs:181:5
   4: test_topology::simple
             at ./tests/test_topology.rs:17:5
   5: test_topology::simple::{{closure}}
             at ./tests/test_topology.rs:7:1
   6: core::ops::function::FnOnce::call_once
             at /home/jess/src/rust/library/core/src/ops/function.rs:248:5
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.


failures:
    simple