jobs listing format + subshell spacing (batch88)

[brianjfox]

Summary

Two related formatting fixes (jobs 83 → 67, comsub2 35 → 27, zero regressions).

1. jobs listing format

The jobs listing diverged from bash in three ways:

• the status field was padded to 22 columns instead of bash's 27 (LONGEST_SIGNAL_DESC);
• every job was marked + instead of + for the current job, - for the previous, and a space otherwise;
• a running background job was missing its trailing &.

Now pads the status to 27, marks the two most recently started jobs +/- (an approximation of bash's current/previous job), and appends & to a running background job.

2. subshell spacing

The single-line AST printer emitted (list) without the spaces bash uses. Emit ( list ) to match bash's deparser (the multi-line function pretty-printer already spaced it). This also fixed subshells inside command substitutions, hence the comsub2 improvement.

[1]   Running                    sleep 5 &
[2]-  Running                    sleep 5 &
[3]+  Running                    ( sleep 2; exit 4 ) &

Testing

• ctest 22/22
• Scoreboard: jobs 83 → 67, comsub2 35 → 27, zero regressions across the full suite
• Verified listing width/markers/ & and subshell rendering (jobs, declare -f, type, trap) against bash 5.3

Closes #293.