fix(eth): Fix RMII Ethernet not being able to be restarted

[me-no-dev]

This pull request includes changes to the ETHClass::begin method in the libraries/Ethernet/src/ETH.cpp file. The main purpose of these changes is to improve the initialization process of the Ethernet MAC and PHY by storing the created instances in class member variables instead of local variables.

Initialization improvements:

• Changed the mac variable to a class member variable _mac and updated the error handling to use _mac.
• Changed the phy variable to a class member variable _phy and updated the error handling to use _phy.
• Updated the switch cases for different PHY types to assign the new PHY instances to _phy instead of phy.
• Modified the eth_config initialization to use the class member variables _mac and _phy instead of the local variables mac and phy.

[github-actions]

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Generated by 🚫 dangerJS against 5a710be

[github-actions]

Test Results

76 files 76 suites 12m 43s ⏱️
38 tests 38 ✅ 0 💤 0 ❌
241 runs 241 ✅ 0 💤 0 ❌

Results for commit 5a710be.

♻️ This comment has been updated with latest results.

[github-actions]

Memory usage test (comparing PR against master branch)

The table below shows the summary of memory usage change (decrease - increase) in bytes and percentage for each target.

Memory	FLASH [bytes]		FLASH [%]		RAM [bytes]		RAM [%]
Target	DEC	INC	DEC	INC	DEC	INC	DEC	INC
ESP32P4	0	⚠️ +4	0.00	0.00	0	0	0.00	0.00
ESP32S3	0	0	0.00	0.00	0	0	0.00	0.00
ESP32S2	0	0	0.00	0.00	0	0	0.00	0.00
ESP32C3	0	0	0.00	0.00	0	0	0.00	0.00
ESP32C6	0	0	0.00	0.00	0	0	0.00	0.00
ESP32H2	0	0	0.00	0.00	0	0	0.00	0.00
ESP32	💚 -4	0	0.00	0.00	0	0	0.00	0.00

Click to expand the detailed deltas report [usage change in BYTES]

Target	ESP32P4		ESP32S3		ESP32S2		ESP32C3		ESP32C6		ESP32H2		ESP32
Example	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM
Ethernet/examples/ETH_TLK110	⚠️ +4	0	-	-	-	-	-	-	-	-	-	-	💚 -4	0
Ethernet/examples/ETH_W5500_Arduino_SPI	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Ethernet/examples/ETH_W5500_IDF_SPI	0	0	0	0	0	0	0	0	0	0	0	0	0	0
Ethernet/examples/ETH_WIFI_BRIDGE	0	0	0	0	0	0	0	0	0	0	-	-	0	0
Ethernet/examples/ETH_LAN8720	-	-	-	-	-	-	-	-	-	-	-	-	💚 -4	0

[SuGlider]

LGTM