Add hook-info field-shape conformance handlers

[wangyb-A]

Summary

Adds 5 conformance handlers (handlers/plugin/plugin_{invocation_info,operation_info,attempt_info,operation_change,context_info}_shape.py) + template_plugin.yaml entries implementing plugin hook-info FIELD-SHAPE requirements 10-19..10-23 from aws/aws-durable-execution-conformance-tests#72 (land that PR first).

Each handler logs ONE single-line JSON record per hook event: a CANONICAL camelCase DUMP of that hook's own info parameter (None/unexposed fields OMITTED — a missing key fails its assertion). GA note: experimental payload fields (execution input/result, operation result) are still DUMPED when exposed but are not asserted by the requirements.

Live validation (us-west-2): 22/23 — ONE DELIBERATE FAILURE (SDK parity gap, tracked in #617)

• ❌ 10-19: Python's invocation infos expose no operations map and no externally-updated-operations collection (JS exposes both on every invocation hook). The dump omits those keys, failing the map-count assertions.
• ✅ 10-20..10-23 pass, plus the entire 10-1..10-18 regression.

[wangyb-A]

Rebased onto plugin-parity-invocation-info (#623) and retargeted; force-pushed 7537017 -> 81e6e3b.

Rationale: the 10-19 handler dumps operationsCount / updatedOperationsCount, which read info.operations and info.updated_operations — fields that #623 adds. So the SDK parity fix has to land first, and this PR is now stacked on it. Two handler commits moved here from the (now closed) #622, where they had been incorrectly bundled with the SDK change.

The branch was previously based on a main that was 3 commits behind, so this also picks up #620/#621/#612. Handler file contents are byte-identical to before the rebase; the diff against the new base is the 6 handler files only, +646/-0. GitHub should auto-retarget this to main once #623 merges.