Improve code readability

[maxim-uvarov]

> git diff (git describe --tags --abbrev=0 HEAD) HEAD -- nudoc/run.nu | aichat 'summarize changes'
The changes made are as follows:

1. Updated the comments and the description of the function to be more clear and descriptive.
2. Changed the default output file extension from any file to specifically a .md file.
3. Modified the assemble-script function to handle errors and enclose > commands into try blocks to avoid errors and output their messages.
4. Added a new function backup-file to create a backup of the file before overwriting it.
5. Added new functions escape-quotes, nudoc-block, highlight-command, trim-comments-plus, try-append-echo-in, try-handle-errors, and execute-code.
6. Updated the assemble-script function to make use of the new functions added.
7. Added a new function parse-block-index to parse the block index from the Nu output lines.
8. Updated the assemble-results function to utilize the new functions and provide a more refined output.