fix(analytics): Pass hashes as list of bytes for On-device conversion measurement

[gilnobrega-tide]

Description

Fixes #17790

THIS IS A DRAFT

Replace this paragraph with a description of what this PR is doing. If you're modifying existing behavior, describe the existing behavior, how this PR is changing it, and what motivated the change.

Related Issues

Replace this paragraph with a list of issues related to this PR from the issue database. Indicate, which of these issues are resolved or fixed by this PR. Note that you'll have to prefix the issue numbers with flutter/flutter#.

Checklist

Before you create this PR confirm that it meets all requirements listed below by checking the relevant checkboxes ([x]).
This will ensure a smooth and quick review process. Updating the pubspec.yaml and changelogs is not required.

• I read the Contributor Guide and followed the process outlined there for submitting PRs.
• My PR includes unit or integration tests for all changed/updated/fixed behaviors (See Contributor Guide).
• All existing and new tests are passing.
• I updated/added relevant documentation (doc comments with ///).
• The analyzer (melos run analyze) does not report any problems on my PR.
• I read and followed the Flutter Style Guide.
• I signed the CLA.
• I am willing to follow-up on review comments in a timely manner.

Breaking Change

Does your PR require plugin users to manually update their apps to accommodate your change?

• Yes, this is a breaking change.
• No, this is not a breaking change.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[MichaelVerdon]

Is this only happening on iOS? Maybe it is something we can get away with just editing the native code, doubt we need to regenerate Pigeons.

[gilnobrega-tide]

@MichaelVerdon
Yes Firebase's On-device conversion measurement is only implemented in iOS

Apologies for not providing more details in this PR
Once the issue is confirmed and reproduced by someone in the team we can discuss the best approach more thoroughly
(Maybe it's not an issue and I misunderstood the flutterfire documentation)

[gilnobrega-tide]

Fixed by #17807