feat: add T value() and set_value(T) fixed_point_scalar_device_view

[jayshrivastava]

Description

This change adds genericT value() and set_value(T) methods to fixed_point_scalar_device_view bringing it up to parity with fixed_width_scalar_device_view.

Closes #8455

Checklist

• I am familiar with the Contributing Guidelines.
• New or existing tests cover these changes.
• The documentation is up to date with these changes.

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ℹ️ Recent review info

⚙️ Run configuration

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Plan: Enterprise

Run ID: 0796826f-d3b7-4d0a-bc19-9a11030a204d

📥 Commits

Reviewing files that changed from the base of the PR and between 3a3a522 and 95e13be.

📒 Files selected for processing (2)

• cpp/include/cudf/scalar/scalar_device_view.cuh
• cpp/tests/scalar/scalar_device_view_test.cu

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📝 Walkthrough

Summary by CodeRabbit

• New Features

  • Added scale-aware fixed-point value access and assignment for device-side scalar views.
  • Fixed-point values can now be read as their numeric type and written with automatic rescaling.

• Tests

  • Added coverage for fixed-point values, scales, direct representation updates, and cross-scale conversions.

Walkthrough

The fixed-point scalar device view now provides scale-aware value retrieval and assignment while retaining direct representation storage. Typed CUDA tests cover value access, scale reporting, direct representation updates, and rescaling across target scales.

Changes

Fixed-point device view

Layer / File(s)	Summary
Scale-aware device API cpp/include/cudf/scalar/scalar_device_view.cuh	Adds fixed-point support documentation and dependency declarations, plus device-side value() and scale-aware set_value(T) operations.
Fixed-point device validation cpp/tests/scalar/scalar_device_view_test.cu	Adds typed CUDA tests for fixed-point value access, direct representation assignment, and rescaled assignments across differing scales.

Estimated code review effort: 3 (Moderate) | ~20 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title is specific and matches the main change: adding generic fixed-point value accessors to fixed_point_scalar_device_view.
Description check	✅ Passed	The description accurately describes the new methods, tests, and parity goal for fixed_point_scalar_device_view.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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