Fix tab completion: quoted output broke matches

[mottelet]

Summary

Tab completion in a notebook cell ran completion(\"obj\") directly and parsed Scilab's own console echo of the result. That echo used to be an unquoted, bracketed format Scilab dropped at least ~2 years ago in favor of displaying string arrays quoted ("a" "b" ...), which the parsing here was never updated for — so every completion candidate comes back wrapped in literal double quotes, and (per the original report) the old fallback also used to open the JavaHelp browser as a side effect on some versions.

Fixed by using printf("%s\n", completion(...)) instead, which prints each match bare, one per line, sidestepping Scilab's own display formatting entirely.

Two things needed care:

• printf errors out on an empty array, so it's only called when completion() isn't empty — checked without ever assigning the result to a variable, since get_completions() runs in the same persistent Scilab session as the user's own code, and a temp variable could shadow one of theirs.
• Scilab's terminal control codes end up glued to the front of the first line of any console output. With the old quoted/bracketed format this only ever landed on a line that got filtered out by coincidence (a substring match against info['obj']); with printf's plain output it could leak into a real match — reproduced with a single-match completion (e.g. "getscilabkeyword" returned "\x1b[4l \x08\x1b[0mgetscilabkeywords" instead of "getscilabkeywords"). Now stripped via a small regex before parsing.

Also includes the same pre-existing ruff cleanup as #58 (this branch was cut from master, which still has that debt) — CI was failing on unrelated pre-existing findings before this cleanup, same as described there.

Test plan

• Verified against a live kernel: multi-match ("plo"), single-match ("getscilabkeyword"), and no-match ("zzzzzz") completions all return clean, unquoted results.
• Confirmed via who_user() that nothing is left behind in the Scilab session after completion runs.
• ruff check . clean, all files py_compile, kernel smoke-tested (disp, %plot producing real output).

🤖 Generated with Claude Code

[mottelet]

Merged into #58 so both fixes land together — closing this one in favor of that. See #58 for the combined changes and updated description.