refactor: share PyTime conversions with time.sleep - #9362

Summary

Share the existing CPython-style PyTime conversion implementation with production time.sleep instead of maintaining the same conversion twice.

• Move the landed numerical helper from _testinternalcapi/pytime.rs to time/pytime.rs and reuse from_seconds_object(..., Round::Up) in sleep.
• Preserve every conversion body, the existing _testinternalcapi argument-binding and diagnostics, and the sleep audit, negative-duration rejection, and platform backends.
• No dependency, Lib, test, thread-lifecycle, or public Python API changes. This is a behavior-preserving extraction from Integrate remaining Python 3.15 final runtime and libraries #8954, not a new numeric feature.

Validation

• Locked/offline VM library check: passed.
• Locked/offline strict VM library Clippy: passed.
• Fresh default CLI build: passed.
• Existing test.test_time.TimeTestCase.test_sleep_exceptions: passed on a fresh, independently sealed binary. This selects only conversion-error and negative-duration cases; no positive sleeps, explicit signal delivery, thread/process creation, or full-module run. Normal interpreter/import initialization is unchanged.

Local validation is based on ef6e2dbaee626e7ea2f24900867fcd4f5aa6ab56. The patch merges cleanly with main b7bebe638c8a44dc2a7ec90cfd6c17912ec88876; its newer memmap2/object dependency graph has not been rebuilt locally and is left to current-merge CI. The full workspace/C-API suites were not run.

Source comparison uses CPython 3.15's object conversion and timeout-rounding contract. The full numerical fixture classes are unavailable on this main baseline; no skipped class is counted as coverage.

AI assistance: OpenAI Codex assisted with the extraction, source review, and validation preparation.