[Backport 2026.1] feat(monkey): extract encryption nemeses into own module

[scylladbbot]

• New file sdcm/nemesis/monkey/encryption.py (222 lines): EnableDisableTableEncryptionBaseMonkey holds the shared _enable_disable_table_encryption() logic (AWS KMS setup, encrypted table create/write/read via scylla-bench, optional key rotation, disable+verify), with two thin subclasses — EnableDisableTableEncryptionAwsKmsProviderWithRotationMonkey and ...WithoutRotationMonkey.
• sdcm/nemesis/init.py: 5473→5299 lines (-174). Removed both disrupt_* methods and the _enable_disable_table_encryption helper; pruned now-unused imports (AwsKms, ScyllaBenchEvent, cql_quote_if_needed) and a leftover breadcrumb comment.
• sdcm/nemesis/monkey/init.py: 920→900 lines (-20). Removed the two thin Monkey classes (auto-discovered via the existing pkgutil.walk_packages mechanism — no manual import needed). Also removed the dead target_pool = NEMESIS_TARGET_POOLS.all_nodes line, since @target_all_nodes already sets that same attribute (DISRUPT_POOL_PROPERTY_NAME == "target_pool") — confirmed with the advisor this was pure copy-paste noise, not needed for backward compat.
• New tests unit_tests/unit/nemesis/monkey/test_encryption.py (9 tests): AWS-backend guard, @scylla_versions guard, full with/without-rotation disrupt flows, user_info_encryption skip-disable path, and class flags.

Key technical point for future phases: this is the first migration of a @scylla_versions-decorated method into a monkey class. The decorator internally does getattr(cls_self, "cluster", cls_self), so I added a cluster property on the base monkey (return self.runner.cluster) — verified experimentally that this satisfies the decorator correctly. Worth reusing for Phase 4 (disrupt_mgmt_restore) and Phase 10 (compaction), which also carry @scylla_versions.

Closes: SCT-213

Testing

• EnableDisableTableEncryptionAwsKmsProviderWithRotationMonkey
• EnableDisableTableEncryptionAwsKmsProviderWithoutRotationMonkey

PR pre-checks (self review)

• I added the relevant backport labels
• I didn't leave commented-out/debugging code

Reminders

• Add New configuration option and document them (in sdcm/sct_config.py)

• Add unit tests to cover my changes (under unit-test/ folder)

• Update the Readme/doc folder relevant to this change (if needed)

• (cherry picked from commit 81cd900)

Parent PR: #15607

[scylladbbot]

@cezarmoise - This PR has conflicts, therefore it was moved to draft
Please resolve them and mark this PR as ready for review by removing the conflicts label