PERF: Lazily load all package exports

[richlundeen]

Summary

• migrate remaining exported pyrit/**/__init__.py packages to the shared PEP 562 lazy-export contract
• preserve package APIs, aliases, object identity, transformer warning suppression, and show_versions compatibility
• explicitly materialize dataset and scenario catalogs only when complete discovery is requested
• retain the intentional GCG experimental-warning import side effect

Depends on microsoft#2455.

Cold start performance

Cold Start Benchmark	Before Change	After Change	Faster
Text matching scorers	7.654465s	6.115633s	20.1%
ROT13/Base64/Base2048 converters	4.986345s	0.562701s	88.7%
import pyrit.memory	5.448382s	0.094392s	98.3%
import pyrit.datasets	8.121517s	0.094086s	98.8%

Each result is the median of seven fresh-process runs.