PPPClass: Add configurable boot delay after reset sequence

[gonzabrusco]

Description of Change

This Pull Request introduces a configurable boot delay after the modem reset sequence in PPPClass.

Previously, the code assumed that the modem would be ready to communicate approximately 100 ms after reset, which is not always true for some modules. In particular, with the SIMCom SIM7070, the modem may still be booting and not yet responsive to AT commands at that point.

To address this, a new _boot_delay parameter was added and integrated into the reset flow. This delay is applied after releasing the reset pin and before attempting to initialize the DCE or synchronize with the modem, ensuring that the modem has sufficient time to complete its boot process.

Test Scenarios

1. Reset pin connected and controlled by PPP.setResetPin()
2. Verified modem behavior with and without extended boot delay
3. Confirmed that without the additional delay the modem may fail to respond to initial AT synchronization
4. Confirmed stable and repeatable PPP startup when the boot delay is applied

Related links

#12314

These captures show the behavior with and without the boot delay commit. The time during which PWRKEY is held low for the SIM7070 to perform a reset is approximately 12.5 seconds. After the reset sequence completes, the modem requires an additional ~5 seconds to finish booting before it becomes responsive to AT commands.

Without accounting for this boot time, the PPP initialization may start too early, causing synchronization failures. The added boot delay ensures that the modem is fully operational before esp_modem_sync() and subsequent PPP initialization steps are executed.

Captures.zip

[github-actions]

Warnings

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Generated by 🚫 dangerJS against 5967e9f

[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
ESP32	0	0	0.00	0.00	0	0	0.00	0.00
ESP32C3	0	⚠️ +10	0.00	0.00	0	⚠️ +16	0.00	⚠️ +0.05
ESP32C5	0	⚠️ +10	0.00	0.00	0	⚠️ +16	0.00	⚠️ +0.03
ESP32C6	0	⚠️ +10	0.00	0.00	0	0	0.00	0.00
ESP32H2	0	⚠️ +10	0.00	0.00	0	⚠️ +16	0.00	⚠️ +0.08
ESP32P4	0	⚠️ +10	0.00	0.00	0	⚠️ +16	0.00	⚠️ +0.06
ESP32S2	0	⚠️ +4	0.00	0.00	0	0	0.00	0.00
ESP32S3	0	⚠️ +4	0.00	0.00	0	0	0.00	0.00

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

Target	ESP32		ESP32C3		ESP32C5		ESP32C6		ESP32H2		ESP32P4		ESP32S2		ESP32S3
Example	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM	FLASH	RAM
libraries/PPP/examples/PPP_Basic	0	0	⚠️ +10	0	⚠️ +10	0	⚠️ +10	0	⚠️ +10	⚠️ +16	⚠️ +10	⚠️ +16	⚠️ +4	0	⚠️ +4	0
libraries/PPP/examples/PPP_WIFI_BRIDGE	0	0	⚠️ +10	⚠️ +16	⚠️ +10	⚠️ +16	⚠️ +10	0	-	-	⚠️ +10	0	0	0	⚠️ +4	0

[github-actions]

Test Results

 91 files   91 suites   31m 30s ⏱️
 67 tests  67 ✅ 0 💤 0 ❌
684 runs  684 ✅ 0 💤 0 ❌

Results for commit 5967e9f.