feat: Support `SProd` and `CompositeOp` for expval

[speller26]

Issue #, if available:

253

Description of changes:

Testing done:

Merge Checklist

Put an x in the boxes that apply. You can also fill these out after creating the PR. If you're unsure about any of them, don't hesitate to ask. We're here to help! This is simply a reminder of what we are going to look for before merging your pull request.

General

• [x] I have read the CONTRIBUTING doc
• [x] I used the commit message format described in CONTRIBUTING
• [x] I have updated any necessary documentation, including READMEs and API docs (if appropriate)

Tests

• [x] I have added tests that prove my fix is effective or that my feature works (if appropriate)
• [x] I have checked that my tests are not configured for a specific region or account (if appropriate)

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 100.00%. Comparing base (b154dce) to head (15012c2). Report is 1 commits behind head on main.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #275 +/- ## ========================================= Coverage 100.00% 100.00% ========================================= Files 7 7 Lines 1242 1244 +2 Branches 305 302 -3 ========================================= + Hits 1242 1244 +2 ```

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.

[speller26]

@astralcai Feel free to check if this implementation makes sense.

[astralcai]

Since it's passing PL integration tests I say it's good.