ci: update pinned development tools

[megabyde]

Summary

• update Conan to 2.31.1 and clang-format/clang-tidy to LLVM 22.1.8
• update gcovr, Prettier, markdownlint-cli2, and Ruff
• document the Python 3.10+ requirement for gcovr 8.6

Upstream highlights

• Conan 2.30-2.31 adds newer GCC settings, CMakeConfigDeps fixes, graduated workspace support, and a 2.31.1 fix for no-op replacements
• LLVM 22 adds clang-tidy checks and improves non-system header diagnostics; the existing wildcard configuration picks up the new checks
• gcovr 8.6 adds Python 3.14 support, drops Python 3.9, and fixes report merging and function-line handling
• Ruff 0.16 expands its defaults and formatter capabilities; this repository retains its explicit rule selection and Prettier ownership of Markdown
• Prettier 3.9.6 includes parser and quote fixes; markdownlint-cli2 0.23.1 refreshes dependencies and attempted-fix reporting

Validation

• make lock-check with Conan 2.31.1; lockfile unchanged
• Debug and Release builds; 10/10 tests passed in each configuration
• make coverage-report with gcovr 8.6; 100% line and function coverage
• make format-check with the updated formatters
• make lint with clang-tidy 22, Ruff 0.16, and markdownlint-cli2 0.23.1
• git diff --check