Sweep core api/ blob_fetcher, date, retry, types (#1975)

* Start sweep of core api/ blob, date, retry, types

Assisted-by: Claude Code:claude-opus-5-5

* Sweep core api/ blob_fetcher, date, retry, types

blob_fetcher: inline format_fetch_result_for into its one public
caller, trim history and restating comments, and collapse 11
duplicate format tests into 3 that compare whole output.

date: the chronological check asserted on its own loop counter;
rename the test to the round trip it really checks.

retry: make the client-only helpers and the retry ceiling private,
inline the timeout constants (pub only for a tautology test), and
cut the module doc that restated the policy field docs.

types: delete 10 serialize-side and round-trip tests that the
payload-deserialize tests already cover.

Assisted-by: Claude Code:claude-opus-5-5

* Fix a missing macro bang in the types test

Assisted-by: Claude Code:claude-opus-5-5

* Pin the batch packages' serialized keys

scan --json writes BatchPackagePatches verbatim, so its serialized
keys are output: compare the whole value instead of the deleted
.contains checks. Also unlink a now-private item from the public
module doc and pin the documented retry ceiling of 10.

Assisted-by: Claude Code:claude-opus-5-5

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Co-authored-by: Claude <noreply@anthropic.com>

Author: mikolalysenko