Add --dry-run flag to CLI (#1967)

[YUVRAJ-SINGH-3178]

Hey! This PR adds a handy --dry-run flag to the CLI as requested in #1967.

It makes it super easy to preview exactly what command a plugin is going to run under the hood, without actually firing off a scan or saving a task to the database.

Here's how it works:

• Added the --dry-run argument to the secuscan scan parser in cli.py.
• If the flag is passed, it uses the plugin_manager to build the command with all the interpolated inputs.
• It also fully simulates the Docker sandbox environment by prepending the exact docker run prefix (with memory/cpu limits) that the executor would normally use.
• Finally, it just prints the final resolved command to the terminal and cleanly exits with a 0 code.

It's great for debugging plugins. Let me know what you think!

[utksh1]

Please rebase this CLI dry-run branch and add focused tests showing it prints the resolved command, never executes the scanner, preserves validation/safe-mode behavior, and returns a useful error for invalid inputs.

[utksh1]

Please add focused CLI tests for --dry-run: it must print the resolved command, return nonzero for an unknown plugin or invalid command, avoid task creation/execution, and reflect Docker wrapping when enabled. Rebase on main afterward.

[utksh1]

Please add focused CLI tests for --dry-run: it must print the resolved command, return nonzero for an unknown plugin or invalid command, avoid task creation/execution, and reflect Docker wrapping when enabled. Rebase on main afterward.

[utksh1]

Please rebase this CLI dry-run branch and add focused tests showing it prints the resolved command, never executes the scanner, preserves validation/safe-mode behavior, and returns a useful error for invalid inputs.

[YUVRAJ-SINGH-3178]

I've completed the --dry-run implementation:

• The CLI now safely bypasses execution and prints the target command when --dry-run is used.
• Added unit tests in test_cli.py to guarantee no background tasks are accidentally spawned.
• Fully rebased onto main to resolve conflicts.