Docs: Fix Sphinx warnings in sys.rst (#108106)

- Mark up named tuple attributes as attributes
- Remove links for external functions
- io.BufferedIOBase has no 'buffer' attribute;
  remove the link and mark up using :attr:`!buffer`
- (Re)format some tables as bullet lists:
  - sys._emscripten_info
  - sys.hash_info
  - sys.int_info
  - sys.thread_info
- In the paragraphs mentioning 'f_trace_lines' and 'f_trace_opcodes',
  add links to the frame objects reference.

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>
Co-authored-by: Adam Turner <9087854+AA-Turner@users.noreply.github.com>