feat: Add scopes, flow-control limit keys and signals

[slinkydeveloper]

New APIs

# Scopes and limit keys (same on ingress client)
fut = ctx.scope("tenant-123").service_call(MyService.handler, arg, limit_key="tenant-123/user42")
ctx.scope("tenant-123").workflow_send(MyWorkflow.run, key, arg)

# generic_call/generic_send with scope (same on ingress client)
ctx.generic_call(service, handler, payload, scope="tenant-123", limit_key="tenant-123/user42")
ctx.generic_send(service, handler, payload, scope="tenant-123")

# Read the inbound scope / limit key / idempotency key
ctx.request().scope
ctx.request().limit_key
ctx.request().idempotency_key

# Await a signal on the current invocation
value = await ctx.signal("approved", type_hint=str)

# Resolve / reject a signal on another invocation
ctx.resolve_signal(invocation_id, "approved", "yes")
ctx.reject_signal(invocation_id, "approved", "denied")

[github-actions]

Test Results

  8 files  ± 0    8 suites  ±0   3m 17s ⏱️ +24s
 60 tests +11   60 ✅ +11  0 💤 ±0  0 ❌ ±0 
267 runs  +51  267 ✅ +51  0 💤 ±0  0 ❌ ±0 

Results for commit 5d11d8d. ± Comparison against base commit 687a78b.

♻️ This comment has been updated with latest results.