Add plural delete_agents alias to agent groups

[rksharma-owg]

Description

TenableIO.agent_groups.delete_agent() already supports removing either one agent or multiple agents, but the plural delete_agents() spelling used by the Nessus interface is unavailable. This adds a thin compatibility alias that delegates to the existing implementation, preserving its validation, single-agent behavior, bulk behavior, and return values.

No dependencies are required.

Fixes #684

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

The regression test was first run against the unmodified implementation and failed with AttributeError. It now verifies that delete_agents() forwards the group ID, all agent IDs, keyword arguments, and return value to delete_agent().

• Focused regression test: uv run --python 3.12 --isolated --group dev pytest -q tests/io/test_agent_groups.py -k delete_agents_alias
• Full local suite: 2,117 passed, 34 skipped, 6 xfailed, 3 xpassed; 95.50% coverage
• Ruff: uv run --python 3.12 --isolated --group dev ruff check tenable
• Fork preflight: Python 3.11, 3.12, 3.13, and 3.14 lint/tests/coverage plus code audit (run)

Test Configuration:

• Python Version(s) Tested: 3.11, 3.12, 3.13, 3.14 on Ubuntu; 3.12.13 on macOS
• Tenable.sc version (if necessary): N/A

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• My changes generate no new warnings
• I have added tests that prove my fix is effective
• New and existing unit tests pass locally with my changes