Add ModalityCombinationsUtil for building modality combination sets

[sarthak-19]

Summary

Adds a new static utility class ModalityCombinationsUtil under src/Messages/Util/ that generates all valid modality combinations from a set of required modalities and a set of optional modalities.

This reduces repetitive, error-prone manual array declarations that provider implementations currently need when registering which input/output modality combinations their models support.

How it works

Uses binary bitmask enumeration to produce all 2^n subsets of the optional modalities, each merged with the fixed required modalities. Because modality lists are unordered, subsets (not permutations) are the correct unit — each combination appears exactly once.

Usage

// All combinations that include text, plus any subset of image/audio/document
$combos = ModalityCombinationsUtil::buildCombinations(
    [ModalityEnum::text()],
    [ModalityEnum::image(), ModalityEnum::audio(), ModalityEnum::document()]
);
// → 8 combinations

// All subsets of text + audio (including the "neither" case)
$combos = ModalityCombinationsUtil::buildCombinations(
    [],
    [ModalityEnum::text(), ModalityEnum::audio()]
);
// → 4 combinations

Issue :

• Add utility to create lists of modality combinations #215

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

If you're merging code through a pull request on GitHub, copy and paste the following into the bottom of the merge commit message.

Co-authored-by: sarthak-19 <sarthak8858@git.wordpress.org>

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 88.16%. Comparing base (6317042) to head (6805f5e).

Additional details and impacted files

@@             Coverage Diff              @@
##              trunk     #225      +/-   ##
============================================
+ Coverage     88.12%   88.16%   +0.03%     
- Complexity     1213     1217       +4     
============================================
  Files            60       61       +1     
  Lines          3934     3945      +11     
============================================
+ Hits           3467     3478      +11     
  Misses          467      467              

Flag	Coverage Δ
unit	88.16% <100.00%> (+0.03%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.