Add policy state metrics and configurable enforce metric labels

[Copilot]

The logger lacked visibility into current policy state and provided insufficient granularity for debugging authorization patterns. No metric tracked loaded policy counts by type, and enforce metrics only exposed allowed and domain labels.

Changes

Policy State Tracking

• New casbin_policy_state_count gauge metric labeled by ptype
• UpdatePolicyState(ptype, count) method to maintain current counts
• Supports arbitrary policy types: p, p2, g, g1, g2, g3, etc.

Configurable Enforce Labels

• New PrometheusLoggerOptions struct with EnforceLabels field
• Three optional label constants: EnforceLabelSubject, EnforceLabelObject, EnforceLabelAction
• NewPrometheusLoggerWithOptions(registry, options) constructor
• Dynamic label value construction in recordEnforceMetrics()

Usage

// Track policy state
logger.UpdatePolicyState("p", 100)
logger.UpdatePolicyState("g", 50)

// Enable fine-grained enforce metrics
options := &prometheuslogger.PrometheusLoggerOptions{
    EnforceLabels: []string{
        prometheuslogger.EnforceLabelSubject,
        prometheuslogger.EnforceLabelObject,
        prometheuslogger.EnforceLabelAction,
    },
}
logger := prometheuslogger.NewPrometheusLoggerWithOptions(registry, options)

Fully backward compatible. Existing constructors use default labels (allowed, domain only).

Original prompt

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This section details on the original issue you should resolve

<issue_title>[Feature] Additional Policy State Metrics & Configurable Enforce Metric Granularity</issue_title>
<issue_description>This proposal adds two observability improvements to casbin-prometheus-logger:

1. Expose current policy counts by type ( p, g, g1, g2 , g3 )
2. Allow optional labels for enforce metrics

Currently, the prometheusLogger focuses on policy operation events (Add / Remove / Load / Save), but lacks visibility into policy state. There is no metric showing how many policy rules are loaded by type, making it hard to monitor permission growth.

In addition, the Enforce metrics are too coarse. casbin_enforce_total only includes allowed and domain (prometheus_logger.go)

enforceTotal: prometheus.NewCounterVec(
			prometheus.CounterOpts{
				Name: "casbin_enforce_total",
				Help: "Total number of enforce requests",
			},
			[]string{"allowed", "domain"},
		),

This makes it difficult to identify high-traffic subjects or debug subject-specific authorization issues.
</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes [Feature] Additional Policy State Metrics & Configurable Enforce Metric Granularity #5

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