Fix typos in documentation

[per1234]

The codespell spellchecker tool is used to automatically detect commonly misspelled words in the files of this project.

The misspelled words dictionary was expanded in the latest release of codespell, which resulted in the detection of a
misspelled word in the project's documentation:

https://github.com/arduino-libraries/Arduino_Threads/actions/runs/13005983050/job/36272909846#step:4:17

Error: ./docs/threadsafe-serial.md:51: pre-emptive ==> preemptive
Codespell found one or more problems

The typo is hereby corrected, which will restore the spell check to a passing state.

---

I supplemented the correction of the automatically detected typo with a general review of the documentation content, fixing the additional typos I identified during that review.

[github-actions]

Memory usage change @ 120e1a9

Board	flash	%	RAM for global variables	%
arduino:mbed_nano:nano33ble	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:mbed_nano:nanorp2040connect	0 - 0	0.0 - 0.0	0 - 0	0.0 - 0.0
arduino:mbed_portenta:envie_m7:target_core=cm7	N/A	N/A	N/A	N/A
arduino:mbed_portenta:envie_m7:target_core=cm4	N/A	N/A	N/A	N/A

Click for full report table

Board	examples/Threading_Basics/Shared_Counter flash	%	examples/Threading_Basics/Shared_Counter RAM for global variables	%	examples/Threading_Basics/Source_Sink_Counter flash	%	examples/Threading_Basics/Source_Sink_Counter RAM for global variables	%	examples/Threading_Basics/Source_Sink_LED flash	%	examples/Threading_Basics/Source_Sink_LED RAM for global variables	%	examples/Threading_Basics/Thermostat flash	%	examples/Threading_Basics/Thermostat RAM for global variables	%	examples/Threadsafe_IO/SPI flash	%	examples/Threadsafe_IO/SPI RAM for global variables	%	examples/Threadsafe_IO/SPI_BusIO flash	%	examples/Threadsafe_IO/SPI_BusIO RAM for global variables	%	examples/Threadsafe_IO/Serial_GlobalPrefixSuffix flash	%	examples/Threadsafe_IO/Serial_GlobalPrefixSuffix RAM for global variables	%	examples/Threadsafe_IO/Serial_ProtocolWrapping flash	%	examples/Threadsafe_IO/Serial_ProtocolWrapping RAM for global variables	%	examples/Threadsafe_IO/Serial_Reader flash	%	examples/Threadsafe_IO/Serial_Reader RAM for global variables	%	examples/Threadsafe_IO/Serial_Writer flash	%	examples/Threadsafe_IO/Serial_Writer RAM for global variables	%	examples/Threadsafe_IO/Wire flash	%	examples/Threadsafe_IO/Wire RAM for global variables	%	examples/Threadsafe_IO/Wire_BusIO flash	%	examples/Threadsafe_IO/Wire_BusIO RAM for global variables	%
arduino:mbed_nano:nano33ble	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0
arduino:mbed_nano:nanorp2040connect	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0	0	0.0
arduino:mbed_portenta:envie_m7:target_core=cm7	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A
arduino:mbed_portenta:envie_m7:target_core=cm4	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A	N/A

Click for full report CSV

Board,examples/Threading_Basics/Shared_Counter<br>flash,%,examples/Threading_Basics/Shared_Counter<br>RAM for global variables,%,examples/Threading_Basics/Source_Sink_Counter<br>flash,%,examples/Threading_Basics/Source_Sink_Counter<br>RAM for global variables,%,examples/Threading_Basics/Source_Sink_LED<br>flash,%,examples/Threading_Basics/Source_Sink_LED<br>RAM for global variables,%,examples/Threading_Basics/Thermostat<br>flash,%,examples/Threading_Basics/Thermostat<br>RAM for global variables,%,examples/Threadsafe_IO/SPI<br>flash,%,examples/Threadsafe_IO/SPI<br>RAM for global variables,%,examples/Threadsafe_IO/SPI_BusIO<br>flash,%,examples/Threadsafe_IO/SPI_BusIO<br>RAM for global variables,%,examples/Threadsafe_IO/Serial_GlobalPrefixSuffix<br>flash,%,examples/Threadsafe_IO/Serial_GlobalPrefixSuffix<br>RAM for global variables,%,examples/Threadsafe_IO/Serial_ProtocolWrapping<br>flash,%,examples/Threadsafe_IO/Serial_ProtocolWrapping<br>RAM for global variables,%,examples/Threadsafe_IO/Serial_Reader<br>flash,%,examples/Threadsafe_IO/Serial_Reader<br>RAM for global variables,%,examples/Threadsafe_IO/Serial_Writer<br>flash,%,examples/Threadsafe_IO/Serial_Writer<br>RAM for global variables,%,examples/Threadsafe_IO/Wire<br>flash,%,examples/Threadsafe_IO/Wire<br>RAM for global variables,%,examples/Threadsafe_IO/Wire_BusIO<br>flash,%,examples/Threadsafe_IO/Wire_BusIO<br>RAM for global variables,%
arduino:mbed_nano:nano33ble,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0
arduino:mbed_nano:nanorp2040connect,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0,0,0.0
arduino:mbed_portenta:envie_m7:target_core=cm7,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A
arduino:mbed_portenta:envie_m7:target_core=cm4,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A,N/A