fix: round-trip serdes result on first run across ops

[ayushiahjolia]

Issue #, if available:
#406
#544

Description of changes:
Extends the step operation's first-run behavior (#543) to the remaining operations: on the first run, an operation now returns the serdes round-tripped value deserialize(serialize(result)) - instead of the raw in-memory result. This is the same value each operation reconstructs
on replay, so results stay identical across the first run and every replay when a non-identity custom SerDes is configured.

Covered operations:

• wait_for_condition: returns the round-tripped state on success.
• run_in_child_context: round-trips in every mode - normal, virtual, and large-payload (ReplayChildren). Large payloads still checkpoint only a compact summary; the full result is round-tripped transiently for the return value. This also flows through map/parallel, whose items and BatchResult go through the child handler.
• invoke and callback need no change (invoke always deserializes from the checkpoint; callback returns only an id).

Testing:

• Covered by unit test, integration test and cloud examples.

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