ci: limit bindgen workflows to relevant paths

[pwltr]

Summary

• add path filters to the iOS and Android bindgen workflows
• keep manual workflow_dispatch runs available for forced validation
• include source, build scripts, platform binding inputs, and each workflow file in the trigger paths

Validation

• ruby -e "require 'yaml'; %w[.github/workflows/ios-bindgen.yml .github/workflows/android-bindgen.yml].each { |f| YAML.load_file(f); puts "ok #{f}" }"
• git diff --check