[mustache_template] Add example app

[princesoni18]

Adds an example application for the mustache_template package and updates the README to be more high-level.

Previously the package had no example app (causing a pub.dev score deduction), and most of the documentation lived in the README. This PR moves the detailed examples into a proper example/ directory and cleans up the README.

Fixes flutter/flutter#183936

Pre-Review Checklist

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• I read the AI contribution guidelines and understand my responsibilities, or I am not using AI tools.
• I read the Tree Hygiene page, which explains my responsibilities.
• I read and followed the Flutter style guide and ran the auto-formatter.
• I signed the CLA.
• The title of the PR starts with the name of the package surrounded by square brackets, e.g. [vector_math]
• I linked to at least one issue that this PR fixes in the description above.
• I followed the version and CHANGELOG instructions, using semantic versioning and the repository CHANGELOG style, or I have commented below to indicate which documented exception this PR falls under¹.
• I updated/added any relevant documentation (doc comments with ///).
• I added new tests to check the change I am making, or I have commented below to indicate which test exemption this PR falls under¹.
• All existing and new tests are passing.

This PR only adds an example app and improves documentation. It does not change any package code, so no version bump or CHANGELOG entry is required. It also falls under the test exemption for pure documentation / example changes.

Footnotes

1. Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling. ↩ ↩²

[gemini-code-assist]

Code Review

This pull request adds a new example package for mustache_template, including a main.dart file with usage examples and a pubspec.yaml file, and updates the .gitignore to exclude FVM cache. It also updates the README.md to reference these examples using code-excerpt markers. The review feedback highlights discrepancies between the code snippets in README.md and the actual implementations in example/lib/main.dart for exampleUsage, nestedPaths, and lambdasExample, which should be kept in sync.

[stuartmorgan-g]

Thanks for the contribution!

It does not change any package code, so no version bump or CHANGELOG entry is required. It also falls under the test exemption for pure documentation / example changes.

The exemption is for unpublished portions of the example; main.dart is published on pub.dev

Also, this PR does not appear to have had the formatter run on it, as indicated in the checklist, nor does it pass analysis.

[stuartmorgan-g]

Ignores for local tools should be done in your user-level git ignore, not added to the repository.

[stuartmorgan-g]

We don't use lints.

[stuartmorgan-g]

None of this is relevant to the example; just the original code, omitting the main() and print, should be part of the excerpt.

[stuartmorgan-g]

And then more generally, you've significantly changed the structure of all of these examples, making them longer by adding unnecessary boilerplate. The code being excerpted should be structurally the same as it was, with the changes being those necessary to follow style rules.

[stuartmorgan-g]

This reference is not correct. Did you run the excerpting tool, or did you manually copy everything between the files?

[princesoni18]

ok i will make the changes and update it ASAP!!

[stuartmorgan-g]

Regarding your comment in the issue about this PR, you will need to be running a current version of the repository tooling to correctly implement this. Targeting a version of the tooling that is more than three years old won't result in a PR that passes CI.