Add pattern for ESP8266 firmware

[lopqto]

Summary

Pattern file for ESP8266 firmware images, including bootloader and application segment headers.

Reference:

• https://github.com/espressif/esptool/blob/master/esptool/bin_image.py
• https://github.com/esp8266/esp8266-wiki/wiki/

Checklist

• A pattern for this format doesn't exist yet (or this PR improves the existing one)
• The new pattern has been added to the relevant table in the Readme
• The new pattern has a description pragma (#pragma description ESP8266 Firmware Image v1)
• The pattern has a magic pragma for automatic detection (#pragma magic [ 0xE9 ] @ 0x00)
• A test file for this pattern has been added to /tests/patterns/test_data/esp8266.hexpat.bin (~4.2KB)

Note on test file: The test file was created by truncating a sample firmware to remove large user_segment data, keeping only the bootloader header and segments needed for pattern verification. The truncated firmware is not executable but fully validates the pattern implementation.