v1.1.0 of attest_flutter

Flutter widget-test integration for attest: a WidgetTester accessibility audit, raster and text-scale collectors, and gate matchers for CI. Changelog excerpt: ### Added - The raster collector detects icon glyphs (Private Use Area code points) and marks their samples as non-text, so the new attest/non-text-contrastrule (WCAG 1.4.11) can hold them to the 3:1 minimum. Requires attest1.1.0. ### Fixed - A small icon whose contrast is between 3:1 and 4.5:1 is no longer flagged as a text-contrast failure.