fix: Update clang-tidy to include src/tests directory header check

[andrzej-neti]

High Level Overview of Change

Update configuration of the clang-tidy tool to include headers from the src/tests and apply the project style to affected files.

Context of Change

The goal is to improve automated checks for the project.

API Impact

No API changes

[mathbunnyru]

Please, update the PR title, these are the choices: https://github.com/XRPLF/actions/blob/main/.github/workflows/check-pr-title.yml#L24

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 82.3%. Comparing base (a911f90) to head (1525e2a).
⚠️ Report is 3 commits behind head on develop.

Additional details and impacted files

@@            Coverage Diff            @@
##           develop   #7307     +/-   ##
=========================================
- Coverage     82.4%   82.3%   -0.0%     
=========================================
  Files         1011    1011             
  Lines        76330   76330             
  Branches      7318    7316      -2     
=========================================
- Hits         62874   62850     -24     
- Misses       13456   13480     +24     

see 12 files with indirect coverage changes

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[Copilot]

Pull request overview

This PR updates the repository’s clang-tidy configuration so that headers under src/tests are included in the header-filtered checks, and then applies style/clang-tidy-driven cleanups to the affected test helper code to keep the build and checks passing.

Changes:

• Expand .clang-tidy HeaderFilterRegex to include tests (in addition to test) directories.
• Apply clang-tidy/style fixes in src/tests/libxrpl (designated initializers, nested namespace syntax, naming alignment like Account::kMaster, and adding [[nodiscard]] on getters/overrides).
• Add a local suppression for the intentionally-uppercase XRP helper function name.

Reviewed changes

Copilot reviewed 9 out of 9 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/tests/libxrpl/tx/AccountSet.cpp	Uses designated initializers for test case data to satisfy readability/style checks.
src/tests/libxrpl/helpers/TxTest.h	Adds a targeted NOLINT for the XRP helper name under clang-tidy naming rules.
src/tests/libxrpl/helpers/TxTest.cpp	Updates genesis/master account usage to the renamed Account::kMaster.
src/tests/libxrpl/helpers/TestServiceRegistry.h	Applies style updates (nested namespace, member naming) aligned with clang-tidy.
src/tests/libxrpl/helpers/TestFamily.h	Minor style adjustments (nested namespace, [[nodiscard]], pointer usage in reset()).
src/tests/libxrpl/helpers/IOU.h	Formatting/style tweaks in constructor initializer list.
src/tests/libxrpl/helpers/Account.h	Renames master to kMaster and adds [[nodiscard]] to accessors.
src/tests/libxrpl/helpers/Account.cpp	Renames the static definition to Account::kMaster.
.clang-tidy	Updates header filter regex to include headers under tests directories.

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[kuznetsss]

LGTM