Add pin rows to Profile Memory table

[khanak0509]

Fixes #8898

Trace Instances already keeps traced classes at the top (via the checkbox), but Profile Memory didn’t have anything similar

This PR adds a Pin column to Profile Memory. Tap the pin icon on a row and that class stays in the pinned section at the top (under All Classes), with a divider between pinned and the rest of the table, same general idea as Trace Instances, but without turning on allocation tracing

before

after

Pre-launch Checklist

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[gemini-code-assist]

Code Review

This pull request introduces a feature to pin classes to the top of the Profile Memory table in DevTools. The implementation involves updating the AdaptedProfile and ProfileRecord models to track pinning status, adding pinning logic and serialization to the ProfilePaneController, and creating a new _PinColumn for the UI. Review feedback identifies a logical issue where the pinned classes listener is not updated during initialization, suggests improving the stateful widget's resilience to controller changes, and highlights performance concerns regarding redundant builders and inefficient key generation for the table.

[Piinks]

Hey @khanak0509 thanks for contributing! Apologies it looks like this fell through the review cracks. Would you like to still work on this change?

[srawlins]

Code looks good. I want to pull it down and play with it.

[khanak0509]

@Piinks Yes, definitely still want to work on this! Thanks for checking in. @srawlins glad the code looks good, let me know if you'd like me to make any changes or if you have any feedback.