fix(build): emit Android alignment flags from build.rs

[reez]

Pub.dev excludes the hidden native/.cargo directory, while the Native Assets hook previously passed that missing config file to Cargo. This caused builds from the published package to fail.

Replace the shipped Cargo config with an Android-gated native/build.rs that emits the 16 KiB page-alignment linker arguments for the cdylib. This makes the alignment flags apply consistently to Native Assets, CI, and manual Cargo builds without requiring --config.

Also:

• Remove the now unused Cargo build dependencies and config plumbing.
• Keep the build script explicit in Cargo.toml so a missing packaged file fails clearly.
• Allow the Android alignment jobs to reach the NDK build by skipping setup-android’s obsolete default tools package.

[reez]

@Johnosezele (and anyone else that wants to give feedback) does moving the Cargo config to a non hidden path and verifying it in the pub.dev package manifest seem like the right fix, or is there a better Dart packaging convention we should use?

[Johnosezele]

I think moving the file is the right approach. Dart excludes hidden folders like .cargo from published packages, and there isn’t another Dart packaging convention for Cargo config files.

We could keep .cargo/config.toml using .pubignore exceptions, but that’s more fragile. Since the build already tells Cargo where the config is with --config, using native/cargo-config.toml seems cleaner.

Only small suggestion: make the CI check verify the exact archived file if possible, rather than matching any file named cargo-config.toml.

[Johnosezele]

Only tradeoff I see is that direct Cargo builds from native/ will no longer discover the config automatically, so those builds must also pass --config.

[reez]

@Johnosezele

Thanks your note about direct Cargo builds led me to prototype a different approach.

I’ve replaced the shipped Cargo config with an Android-gated build.rs, so Native Assets and manual Cargo builds receive the alignment flags without --config. This definitely changes the implementation you reviewed.

I also included a two line fix for the alignment jobs, which currently fail in setup-android before reaching the build. I may actually spin that CI only change into a separate PR to keep this one focused.

[Johnosezele]

ACK c9133fa