Add task-level cache max age support (#1501)

## Summary

- add `Cache.max_age` as a task-level cache policy, accepting a
nonnegative `timedelta` or integer number of seconds
- serialize the setting to `TaskMetadata.cache_max_age`, preserving the
distinction between unset and explicit zero
- round-trip and override the setting through remote task details
- validate positive, zero, unset, negative, and invalid-type behavior

`None` uses the platform default, zero disables age-based expiration,
and a positive value limits the age of cached results that the task will
reuse.

## IDL dependency

This depends on `TaskMetadata.cache_max_age` from flyteorg/flyte#7938
([commit](flyteorg/flyte@6390805)).
The dependency pin is intentionally not changed in this PR, so CI is
expected to fail against `flyteidl2==2.0.44` until a new IDL version is
published and the SDK pin is bumped.

## Testing

Using a locally built `flyteidl2==2.0.45.dev0` wheel:

- `pytest -q tests/user_api/test_cache.py
tests/flyte/internal/runtime/test_task_serde.py
tests/flyte/remote/test_task.py tests/flyte/test_image.py` — 177 passed
- Ruff passed for all changed source and test files
- `git diff --check` passed

### Dogfood validation

Validated against `dogfood/flytesnacks/development` and the leaseworker
implementation in unionai/cloud#18043. The expiring task template
contained `cacheMaxAge: 60s`; the normal-cache task omitted the field.

| Scenario | Run | Cache status | Execution marker |
|---|---|---|---|
| Initial 60s cache |
[expiring-3](https://dogfood.cloud-staging.union.ai/v2/domain/development/project/flytesnacks/runs/pvditt-cache-age-expiring-3)
| `CACHE_MISS` | `04:46:48.396163Z` |
| Immediate repeat |
[expiring-4](https://dogfood.cloud-staging.union.ai/v2/domain/development/project/flytesnacks/runs/pvditt-cache-age-expiring-4)
| `CACHE_HIT` | Same marker |
| Repeat after 163s |
[expiring-5](https://dogfood.cloud-staging.union.ai/v2/domain/development/project/flytesnacks/runs/pvditt-cache-age-expiring-5)
| `CACHE_MISS` | `04:49:31.529448Z` |
| Immediate repeat of refreshed result |
[expiring-6](https://dogfood.cloud-staging.union.ai/v2/domain/development/project/flytesnacks/runs/pvditt-cache-age-expiring-6)
| `CACHE_HIT` | Same refreshed marker |
| Normal cache initial |
[normal-1](https://dogfood.cloud-staging.union.ai/v2/domain/development/project/flytesnacks/runs/pvditt-cache-age-normal-1)
| `CACHE_MISS` | `04:47:39.246597Z` |
| Normal cache immediate repeat |
[normal-2](https://dogfood.cloud-staging.union.ai/v2/domain/development/project/flytesnacks/runs/pvditt-cache-age-normal-2)
| `CACHE_HIT` | Same marker |
| Normal cache after the wait |
[normal-3](https://dogfood.cloud-staging.union.ai/v2/domain/development/project/flytesnacks/runs/pvditt-cache-age-normal-3)
| `CACHE_HIT` | Still the original marker |

Dogfood workers were still using an older SDK without the task-side
constructor argument, so the probe used this SDK build for registration
and an import-time compatibility guard for the older task runtime. Cache
lookup and expiration occur in leaseworker before task execution.

---------

Signed-off-by: Paul Dittamo <pvdittamo@gmail.com>

Author: pvditt