add in-memory ASF request dispatching for boto clients

[bentsku]

Motivation

Taken from #7396 from @thrau:
This PR adds code to make calls from boto clients directly to a Gateway without an HTTP server roundtrip. This can make internal calls much faster because they don't require IO.

The mechanism used to achieve this is botocore's before-send event, which can be used to short-circuit the request logic by returning a response from the event handler, before the HTTP request is even made.

I did some basic refactoring to make this easier, including:

• created localstack.runtime.components as a place for runtime-level singleton components
• added a new method to Gateway with the signature def handle(self, context: RequestContext, response: Response), which now makes the Gateway a drop-in replacement for a handler chain (and easier to call if you want to invoke it with a pre-existing RequestContext).

I believe we could merge this as is, as it's only opt-in, and we could improve in follow-up iterations. We'd at least get a preview version of it, and we can give it more tries.

Benchmarks:

Results:

	Base	In-memory client	Everything (#9568) + in-memory
Throughput for 1kb publish (req/s)	20.17	28.98	102.77

In-memory only with cloudwatch SQS metrics + SNS delivery logs: 1000 requests took 34.5011 s = 34.5011 ms/op = 28.98 req/sec
All fixes: 1000 requests took 9.7307 s = 9.7307 ms/op = 102.77 req/sec

Testing

Ext Integration Tests 6506 ✅
Successful run with the flag enabled: https://app.circleci.com/pipelines/github/localstack/localstack/25062/workflows/401a985e-e287-483e-82f3-229daf251654

TODO:

• basic PoC implementation
• integration with the client factory and connect_to
• more benchmarks to see whether/where this is really useful
• documentation

[github-actions]

S3 Image Test Results (AMD64 / ARM64)

  2 files  ±0    2 suites  ±0   3m 14s ⏱️ +3s
401 tests ±0  351 ✅ ±0   50 💤 ±0  0 ❌ ±0 
802 runs  ±0  702 ✅ ±0  100 💤 ±0  0 ❌ ±0 

Results for commit 430d6fc. ± Comparison against base commit 7295eb3.

♻️ This comment has been updated with latest results.

[github-actions]

LocalStack Community integration with Pro

    2 files      2 suites   1h 43m 15s ⏱️
3 004 tests 2 695 ✅ 309 💤 0 ❌
3 006 runs  2 695 ✅ 311 💤 0 ❌

Results for commit e8a9390.

♻️ This comment has been updated with latest results.