Add Rust multiple section types example

[Copilot]

Problem

Users reported being unable to find a Rust example for multiple section types, despite examples existing for Go, Node, and Java implementations. This created confusion about whether casbin-rs supports this feature.

Reference: https://casbin.org/docs/syntax-for-models#multiple-section-types

Solution

Added a comprehensive, runnable example demonstrating multiple section types support in casbin-rs.

What's New

examples/multi_section.rs - A standalone example showing:

• How to use multiple section types in a single model
• Section 1 (default): Three-parameter model (subject, action, object)
• Section 2: Two-parameter model (subject, action)
• How to use EnforceContext to switch between sections

Updated README.md - Added "Multiple section types" entry to the examples table

Example Usage

use casbin::prelude::*;
use casbin::EnforceContext;

let e = Enforcer::new(
    "examples/multi_section_model.conf",
    "examples/multi_section_policy.csv",
).await?;

// Use default section (Section 1)
e.enforce(("alice", "read", "project1"))?;

// Use Section 2 via EnforceContext
let ctx = EnforceContext::new("2");
e.enforce_with_context(ctx, ("james", "execute"))?;

Why This Matters

This example:

• ✅ Demonstrates that casbin-rs fully supports multiple section types
• ✅ Provides parity with other Casbin language implementations
• ✅ Includes clear documentation on how policies and matchers work
• ✅ Works with both tokio and async-std runtimes

Users can now easily discover and understand how to use multiple section types in their Rust projects.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>rust multiple section types example</issue_title>
<issue_description>I found multiple section types example with go、node 、java. but can't find rust, does rust support multiple section type?
https://casbin.org/docs/syntax-for-models#multiple-section-types</issue_description>

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

• Fixes rust multiple section types example #318

---

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[github-actions]

Benchmark for 2bf5287

Click to view benchmark

Test	PR Benchmark	Master Benchmark	%
b_benchmark_rbac_model_large	9.4±0.04ms	10.2±0.03ms	-7.84%
benchmark priority model	4.1±0.09µs	4.1±0.05µs	0.00%
benchmark_abac_model	2.5±0.03µs	2.5±0.03µs	0.00%
benchmark_basic_model	3.6±0.05µs	3.6±0.03µs	0.00%
benchmark_key_match	7.2±0.07µs	7.3±0.19µs	-1.37%
benchmark_raw	0.0±0.00ns	0.0±0.00ns	NaN%
benchmark_rbac_model	5.9±0.09µs	6.0±0.05µs	-1.67%
benchmark_rbac_model_medium	788.9±8.58µs	850.8±15.24µs	-7.28%
benchmark_rbac_model_with_domains	5.8±0.09µs	5.7±0.08µs	+1.75%
benchmark_rbac_with_deny	8.1±0.10µs	8.3±0.11µs	-2.41%
benchmark_rbac_with_resource_roles	4.3±0.06µs	4.3±0.08µs	0.00%
benchmark_role_manager_large	4.3±0.07ms	4.3±0.01ms	0.00%
benchmark_role_manager_medium	271.1±2.47µs	269.1±2.27µs	+0.74%
benchmark_role_manager_small	84.0±1.42µs	92.1±1.32µs	-8.79%

[github-actions]

Benchmark for 2bf5287

Click to view benchmark

Test	PR Benchmark	Master Benchmark	%
b_benchmark_rbac_model_large	9.9±0.02ms	9.7±0.10ms	+2.06%
benchmark priority model	4.1±0.09µs	4.1±0.04µs	0.00%
benchmark_abac_model	2.5±0.02µs	2.5±0.04µs	0.00%
benchmark_basic_model	3.6±0.03µs	3.6±0.04µs	0.00%
benchmark_key_match	7.5±0.10µs	7.4±0.09µs	+1.35%
benchmark_raw	0.0±0.00ns	0.0±0.00ns	NaN%
benchmark_rbac_model	6.1±0.24µs	5.9±0.10µs	+3.39%
benchmark_rbac_model_medium	823.2±8.19µs	800.3±8.47µs	+2.86%
benchmark_rbac_model_with_domains	5.8±0.04µs	5.7±0.07µs	+1.75%
benchmark_rbac_with_deny	8.3±0.11µs	8.2±0.06µs	+1.22%
benchmark_rbac_with_resource_roles	4.3±0.06µs	4.3±0.04µs	0.00%
benchmark_role_manager_large	4.4±0.03ms	4.2±0.01ms	+4.76%
benchmark_role_manager_medium	294.5±6.77µs	267.3±3.22µs	+10.18%
benchmark_role_manager_small	88.0±0.88µs	85.4±1.84µs	+3.04%