Fix Rp2040 cyw43 firmware build bug

[mikee47]

Bad Rp2040 cyw43 firmware build bug, introduced in #2804.

Also ensure builds work with previous 10.3.1 toolchain.

[what-the-diff]

PR Summary

• Improved File Size Calculation Function
  The write_chunk function, which is important for understanding the size of each file in our project, was adjusted to compute the file size more accurately. This could help us manage our storage usage better.

• Adjusted Linker Flags with Compiler Version Consideration
  The settings for our compiler, currently known as 'Linker Flags' (LDFLAGS), have been updated to include -Wl,--no-warn-rwx-segments. This update will only be applied when our compiler's main version isn't equal to 10. This adjustment enables more stable compilations of our code, providing a smoother development process.