[camera_android_camerax] Add presubmit sweep, cross-platform paths, and test diff guidelines to AGENTS.md

[reidbaker-agent]

These suggestions came from /learn. No evals because the infra required to test the actually valuable one requires interactions with remote services. I am going to brainstorm on how we can/should evaluate remote interactions.

http://github.com/flutter/packages/pull/12681 is a pr that will not required the override labels for prs like this.

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Agent authored description

Description

Adds key agent guidelines to camera_android_camerax/AGENTS.md:

• Presubmit Sweep Fixes: Directs agents to wait until all builder targets in the presubmit matrix complete before pushing, reproducing and fixing all failures locally to push in one consolidated commit.
• Cross-Platform Paths in Tests: Enforces constructing CLI arguments and file paths with package:path (p.join / p.joinAll) rather than hardcoded / to avoid test failures on Windows CI bots.
• Preserve Test Order: Directs agents to maintain the original sequence of existing unit tests when adding or updating tests to minimize review diffs.

Tests

• Validated flutter test test/skills_evals_test.dart test/validate_skills_test.dart (all passing).

[gemini-code-assist]

Code Review

This pull request updates the AGENTS.md file in the camera_android_camerax package by adding guidelines for presubmit sweep fixes, cross-platform paths in tests, and preserving test order. The feedback suggests clarifying that the cross-platform path guideline applies to local file system paths and not to Flutter asset paths, package URIs, or URLs, which must always use forward slashes.

[auto-submit]

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