v0.3.11 compatibility: step.authz_check conflicts with built-in type

[intel352]

Problem

Workflow engine v0.3.11 added a built-in step.authz_check step type (via the pipelinesteps plugin). When loading workflow-plugin-authz via engine.LoadPlugin(), the plugin loader rejects it because step.authz_check is already registered:

step type "step.authz_check" already registered

Context

The built-in step.authz_check in v0.3.11 uses a PolicyEngineModule interface, but the only implementation is a "mock" backend (the resolvePolicyEngine() function does a concrete type assertion to *PolicyEngineModule). The external plugin's Casbin-backed implementation is still needed for production use.

Workaround

We bypass engine.LoadPlugin() entirely and register the plugin's factories directly via engine.AddModuleType() / engine.AddStepType(), which silently overwrite the built-in types. See GoCodeAlone/workflow#262 for details.

Suggested Fix

The plugin could check whether its step types are already registered and either:

1. Skip registration of conflicting types (if the built-in is sufficient)
2. Use a different step type name (e.g., step.authz_check_casbin)
3. Coordinate with the engine to allow overrides (pending Plugin loader: allow external plugins to override built-in step types workflow#262)

Related: GoCodeAlone/workflow#262 which is being addressed in GoCodeAlone/workflow#263 (primary changes are already complete in that PR)