Use cpex framework imports

[lucarlig]

Summary

• Rebase branch on latest main and resolve integration-test conflicts while preserving the cpex.framework import migration.
• Replace plugin/test framework imports with cpex.framework modules and keep Rust bridge/shim paths aligned.
• Add cpex>=0.1.0.dev11,<0.2.0 across affected plugin packages and refresh lockfiles.
• Bump plugin versions with consistent metadata (Cargo.toml + plugin-manifest.yaml), normalized to +1 patch over main for each touched plugin.

Version Changes

• encoded_exfil_detection: 0.2.1 -> 0.2.2
• pii_filter: 0.2.1 -> 0.2.2
• rate_limiter: 0.0.4 -> 0.0.5
• retry_with_backoff: 0.2.0 -> 0.2.1
• secrets_detection: 0.2.1 -> 0.2.2
• url_reputation: 0.2.0 -> 0.2.1

Validation

• CI validate-and-detect gate addressed by aligning manifest and Cargo versions.
• Remaining CI jobs run from latest push on fix/use-cpex-framework-dependency.

Closes #58