This commit adds a test for context disasm showing of file descriptors
file paths in syscalls like read() or close().
It also fixes a small issue when Pwndbg is run with PWNDBG_DISABLE_COLORS=1
This issue was that executing:
```
pi '{a:2}'.format(a=pwndbg.color.context.prefix(pwndbg.config.code_prefix))
```
Failed when Pwndbg was run with disabled colors. It failed because our
generate color functions in pwndbg/color/* ended up not processing the
input argument -- which here is a Pwndbg config Paramater object -- so
that we got a very non obvious exception:
```
Exception occurred: context: unsupported format string passed to Parameter.__format__ (<class 'TypeError'>)
```
This issue could hypothetically also exist if our config value would be
empty I think. So with the fix in this commit, where we do str(x) over
the color funciton argument should fix this issue in all cases.