Berry 'serial.read()' read only 'n' bytes

[s-hadinger]

Description:

Add an optional parameter to serial.read( [n : bytes] ) -> bytes() to limit the number of bytes returned. Remaining bytes are kept in the serial internal buffer, to be read later.

Checklist:

• The pull request is done against the latest development branch
• Only relevant files were touched
• Only one feature/fix was added per PR and the code change compiles without warnings
• The code change is tested and works with Tasmota core ESP8266 V.2.7.8
• The code change is tested and works with Tasmota core ESP32 V.3.1.1.250109
• I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass