fix(ci): install Flutter cargo tools explicitly

[Tovli]

Summary

• add a retrying cargo tool installer used by Flutter/Dart CI codegen
• install pinned flutter_rust_bridge_codegen and cargo-expand before make codegen-flutter
• run React Native codegen through a generic retry wrapper to survive transient crates.io EOFs during first-time helper builds
• retry wasm-pack release downloads so transient GitHub 5xx responses do not fail web builds immediately
• add CI guard tests for tool installation, command retry behavior, and workflow wiring
• bump workspace version from 0.3.8 to 0.3.9

Verification

• python tests/check_ci_workflows.py
• bash tests/test-install-cargo-tool.sh
• bash tests/test-retry-command.sh
• git diff --check
• cargo test --locked --workspace
• cargo fmt --check