Add AP mode support to ESP32::WiFi

[yuuu]

Summary

Add AP (Access Point) mode support to the ESP32::WiFi class in picoruby-esp32, so that PicoRuby code on R2P2-ESP32 can start a Wi-Fi access point in addition to the existing station mode.

Background

On the RP2040 / Pico W side, an equivalent change is being introduced for CYW43:

• Add minimal CYW43 AP mode API picoruby#400 - "Add minimal CYW43 AP mode API"

That PR adds the following Ruby APIs:

• CYW43.enable_ap_mode(ssid, password, auth = CYW43::Auth::WPA2_AES_PSK) -> bool
• CYW43.disable_ap_mode() -> bool

We want ESP32::WiFi to expose a comparable AP mode API so that AP mode is available across both RP2040 and ESP32 targets.

Proposed API

Modeled after picoruby/picoruby#400, on the ESP32::WiFi class:

• ESP32::WiFi.enable_ap_mode(ssid, password, auth = <ESP32 default WPA2>) -> bool
• ESP32::WiFi.disable_ap_mode() -> bool

The exact constant name(s) for the auth mode should match existing ESP32::WiFi conventions.

Approach

• Reference the design and API shape of Add minimal CYW43 AP mode API picoruby#400.
• Implement the AP-mode bindings on top of ESP-IDF's Wi-Fi APIs (esp_wifi_set_mode(WIFI_MODE_AP) etc.).
• Keep the first step minimal: bringing up / tearing down the AP. Higher-level concerns (DHCP server tuning, IP configuration helpers, etc.) can be follow-ups.
• Add a minimal example and note current limitations, mirroring the structure of PR #400.

Example (target usage)

ESP32::WiFi.enable_ap_mode("R2P2-AP", "12345678")
puts "AP started"

References

• Reference PR (RP2040 / CYW43): Add minimal CYW43 AP mode API picoruby#400
• picoruby-esp32: https://github.com/picoruby/picoruby-esp32