fix(cli): warn on duplicate global flags instead of silently last-wins (#243)

[RUNECTZ33]

Summary

Closes #243.

alw view rates --netuid 7 --netuid 8 previously took 8 silently — no indication anywhere that 7 was discarded. parse_global_flags simply overwrote the dict entry on the second match.

Change

Track seen canonical keys in parse_global_flags. On a duplicate, keep the existing last-wins behavior (preserves any operator scripts that depended on it) but surface the override via stderr:

warning: duplicate global flag --netuid '8' overrides earlier --netuid '7'

Same handling for both --flag value and --flag=value forms.

Why warn rather than reject

Issue says "Warn or reject duplicate globals." I picked warn to:

• Avoid breaking existing scripts that may rely on the override pattern (e.g., wrapper scripts that prepend defaults and then accept user overrides).
• Stay parser-side conservative: rejection at parse time would terminate the whole command, often with no obvious recovery for the operator.
• Make the silent failure visible immediately so a typo gets caught at the first run.

If maintainers prefer hard rejection instead, happy to flip — change is one branch in the same function.

Scope

allways/cli/swap_commands/helpers.py: +28 / -2. No new imports (sys already imported). Output goes via print(..., file=sys.stderr) so it doesn't pollute stdout for any tooling that pipes the CLI's normal output.

Test plan

• AST parses cleanly: python3 -c "import ast; ast.parse(...)"
• Logic verified manually:
  • argv=['alw', 'view', 'rates', '--netuid', '7', '--netuid', '8'] → overrides={'netuid': '8'} + stderr warning
  • argv=['alw', 'view', 'rates', '--netuid=7', '--netuid=8'] → same outcome
  • argv=['alw', 'view', 'rates', '--netuid', '7'] → overrides={'netuid': '7'} + no warning
• Confirmed sys.stderr is the right channel — CLI's normal stdout output (rates table, etc.) stays intact for piping.