Bump dart_pub to 0.0.9 to restore pub points

[Rexios80]

Summary

puby 1.39.0 first dropped 160 → 150 after the pana “up-to-date dependencies” grace expired on the exact pin dart_pub: 0.0.8 (latest 0.0.9).

A later pub.dev re-analysis (2026-08-31T20:05:55Z) took the published 1.39.0 from 150 → 70/160. The extra −80 is one timeout cascade, not four separate package bugs:

• dart pub get / dart pub outdated exceeded pana’s 2:00 sandbox timeout
• that made platform detection, dartdoc, analysis, and the outdated-constraint check all fail
• lower-bound pub downgrade still passed on that same run, so the graph itself is solvable

Checked locally on this branch and on published 1.39.0: dart pub get and dart pub outdated --no-dev-dependencies --up-to-date --no-dependency-overrides both finish in ~0.3–1.3s. No resolver loop or hang. 1.39.0’s only real constraint issue is still dart_pub 0.0.8 vs 0.0.9.

dart_pub 0.0.9 is a drop-in for the solver/cache APIs puby uses. The pin stays exact (0.0.9) because dart_pub asks dependents to pin. rexios_lints is bumped to ^18.1.0 so analyzer 14 resolves (dev_dependency only; not scored).

No extra code changes for the −80. Publishing 1.39.1 should restore 160/160: this branch already scores 160/160 with local pana 0.23.18 (same as pub.dev), including get/outdated well inside the 2-minute budget.

Test plan

• dart pub get resolves with dart_pub 0.0.9 and rexios_lints ^18.1.0 (~0.3s)
• Published 1.39.0 dart pub get / outdated also succeed locally (~1.3s); no hang
• dart analyze --fatal-infos is clean
• dart format --set-exit-if-changed . is clean
• dart pub outdated --no-dev-dependencies --up-to-date --no-dependency-overrides shows dart_pub 0.0.9 / latest 0.0.9
• pana --no-warning --exit-code-threshold 0 → 160/160 (re-run 2026-09-01, 63s)
• Dart-only tests (config_test, projects_test, unknown_command_test, exec_test)
• Static Analysis CI (format, analyze, full dart test, pana)