Refactor monitor_rules for better rule processing

[yi-zelin]

Fixes #7326

What's wrong?

nwg-displays generate multi-line formatted Lua monitor configs (where hl.monitor({, output, and scale sit on separate lines).

Because omarchy-hyprland-monitor-clamshell pipes monitors.lua line-by-line into sed, configured_monitor_value() fails to match the regular expression, which expects the entire hl.monitor({ ... }) declaration to reside on a single line. This parsing failure causes read_monitor_scale() to fall back to the default scale = 2, continuously reverting fractional scale configurations.

What does this PR do?

• Updates monitor_rules() to flatten multi-line table declarations into a single stream using tr '\n' ' '.
• Injects a newline before each hl.monitor declaration using sed 's/hl\.monitor/\n&/g'.
• Ensures each monitor definition is isolated onto its own line so the existing downstream regex parser can reliably extract keys without modifying the underlying extraction logic.

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