[ads] [[nodiscard]] code health

[tmancey]

Resolves brave/brave-browser#44062

Submitter Checklist:

• I confirm that no security/privacy review is needed and no other type of reviews are needed, or that I have requested them
• There is a ticket for my issue
• Used Github auto-closing keywords in the PR description above
• Wrote a good PR/commit description
• Squashed any review feedback or "fixup" commits before merge, so that history is a record of what happened in the repo, not your PR
• Added appropriate labels (QA/Yes or QA/No; release-notes/include or release-notes/exclude; OS/...) to the associated issue
• Checked the PR locally:
  • npm run test -- brave_browser_tests, npm run test -- brave_unit_tests wiki
  • npm run presubmit wiki, npm run gn_check, npm run tslint
• Ran git rebase master (if needed)

Reviewer Checklist:

• A security review is not needed, or a link to one is included in the PR description
• New files have MPL-2.0 license header
• Adequate test coverage exists to prevent regressions
• Major classes, functions and non-trivial code blocks are well-commented
• Changes in component dependencies are properly reflected in gn
• Code follows the style guide
• Test plan is specified in PR before merging

After-merge Checklist:

• The associated issue milestone is set to the smallest version that the
  changes has landed on
• All relevant documentation has been updated, for instance:
  • https://github.com/brave/brave-browser/wiki/Deviations-from-Chromium-(features-we-disable-or-remove)
  • https://github.com/brave/brave-browser/wiki/Proxy-redirected-URLs
  • https://github.com/brave/brave-browser/wiki/Fingerprinting-Protections
  • https://github.com/brave/brave-browser/wiki/Brave%E2%80%99s-Use-of-Referral-Codes
  • https://github.com/brave/brave-browser/wiki/Web-Compatibility-Exceptions-in-Brave
  • https://github.com/brave/brave-browser/wiki/QA-Guide
  • https://github.com/brave/brave-browser/wiki/P3A

Test Plan:

[github-actions]

[puLL-Merge] - brave/brave-core@27710

Description

This PR adds the [[nodiscard]] attribute to boolean return functions across the Brave Ads codebase. The [[nodiscard]] attribute indicates that the return value of a function should not be discarded, helping to prevent bugs where important boolean results are accidentally ignored. This is a code quality improvement that helps enforce better error handling and value checking.

Changes

Changes

• Added [[nodiscard]] attribute to boolean return functions in multiple files, organized by component:

1. browser/ui/views/brave_ads/:

   • Modified color_util.h
   • Added attribute to RgbStringToSkColor

2. components/brave_ads/browser/:

   • Modified multiple files including reminder_util.h
   • Added attribute to functions like IsReminder

3. components/brave_ads/core/internal/:

   • Modified multiple utility and helper files
   • Added attribute to functions like DoesRespectCap, IsInitialized, IsEmpty
   • Added to permission rules, condition matchers, and targeting functions

4. components/brave_ads/core/public/:

   • Modified interface files
   • Added attribute to public API functions returning booleans

sequenceDiagram
    participant Compiler as C++ Compiler
    participant Code as Brave Ads Code
    participant Dev as Developer
    
    Dev->>Code: Adds [[nodiscard]] to boolean functions
    Code->>Compiler: Compilation
    Compiler->>Dev: Warning if bool result ignored
    Note over Compiler,Dev: Helps prevent accidental error ignoring
    Dev->>Code: Must handle all boolean returns
    Note over Code,Dev: Improves code quality

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Security Hotspots

None - This is a type system enhancement that doesn't affect runtime behavior.

[github-actions]

Chromium major version is behind target branch (133.0.6943.98 vs 134.0.6998.15). Please rebase.