…r case/format & safer string handling (#4628)

# Description of Changes

- Standardized all locale-sensitive operations to use `Locale.ROOT`:
- Replaced `toLowerCase()/toUpperCase()` and `String.format(...)` with
`Locale.ROOT` variants across services, controllers, utils, and tests
(e.g., `InstallationPathConfig`, `ApplicationProperties`,
`ResourceMonitor`, `ChecksumUtils`, `PdfUtils`, `UploadLimitService`).
- Hardened comparisons and parsing:
- Normalized host/domain and file-extension checks with
`toLowerCase(Locale.ROOT)`; switched several `equals` calls to
constant-first style (e.g., content types, security domain checks).
- Logging & formatting improvements:
- Ensured percent/size values and hex formatting use root-locale
formatting to avoid locale-dependent output.
- Code quality & readability:
  - Converted multiple if/else ladders to modern `switch` expressions.
- Minor refactors (method references, early returns), removed redundant
returns, and clarified log messages.
- Minor fixes/behavioral nits:
- Normalized printer selection by lowercasing the searched name once;
made some equality checks null-safe/constant-first; added missing
`@Override` annotations where appropriate.

## Why

- Consistent use of `Locale.ROOT` avoids surprises in different
user/system locales (e.g., Turkish-I issues), makes string comparisons
deterministic, and keeps numeric/hex formatting stable across
environments.

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## Checklist

### General

- [x] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [x] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [x] I have performed a self-review of my own code
- [x] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

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Co-authored-by: Anthony Stirling <77850077+Frooodle@users.noreply.github.com>
Co-authored-by: James Brunton <jbrunton96@gmail.com>