Simplify Lambda payload parsing

[joe4dev]

Motivation

The code for parsing the JSON payload of a Lambda invocation is unnecessarily cumbersome. It is also used heavily (>150 times across LS and ext). Making such a common task more readable improves maintainability and extensibility (more Lambda service integrations will likely reuse the same code patterns).

Changes

• Apply the following simplification suggested by @thrau: https://github.com/localstack/localstack-ext/pull/2540#discussion_r1464900754

-        events = json.loads(to_str(invoke_result["Payload"].read()))
+        events = json.load(invoke_result["Payload"]))

• Apply minor refactorings to unify usage (e.g., merge or split lines)

[github-actions]

S3 Image Test Results (AMD64 / ARM64)

  2 files    2 suites   3m 13s ⏱️
386 tests 336 ✅  50 💤 0 ❌
772 runs  672 ✅ 100 💤 0 ❌

Results for commit 026820c.

♻️ This comment has been updated with latest results.

[coveralls]

coverage: 83.828% (-0.002%) from 83.83%
when pulling 026820c on simplify-json-loading
into 04d92da on master.

[github-actions]

LocalStack Community integration with Pro

    2 files      2 suites   1h 21m 8s ⏱️
2 633 tests 2 386 ✅ 247 💤 0 ❌
2 635 runs  2 386 ✅ 249 💤 0 ❌

Results for commit 026820c.

♻️ This comment has been updated with latest results.

[calvernaz]

LGTM, thanks for tackling this 🚀

[macnev2013]

LGTM 🚀