Add C linter/formatter (clang-format + clang-tidy) to CI

[matapatos]

Summary

• Adds a new lint-c GitHub Actions job to lint and format the C sources of the PHP extension, alongside the existing PHP test matrix.
• clang-format (formatter, failing): adds a .clang-format config derived from the repo's existing C style (4-space indent; custom brace wrapping — function braces on a new line, control/struct/enum braces attached) and reformats all .c/.h files so clang-format --dry-run --Werror passes immediately. The CI step runs the dry-run check.
• clang-tidy (static analyzer, report-only): adds a .clang-tidy config with a conservative, Zend-macro-aware check set (bug-finding + performance + readability). Runs against the extension sources listed in config.m4 using a compile_commands.json generated via bear -- make. Set to report-only (WarningsAsErrors empty) so the existing, never-tidied code is not blocked — findings surface in CI logs to be addressed over time.
• Adds Taskfile tasks mirroring the existing lint/test:lint convention: lint:c:format (writes), test:c:format (check), test:c:tidy (analysis). test:c:format is wired into the test aggregator.
• Ignores compile_commands.json (Bear build artifact).

Notes on choices (decided with the user)

• Tools: clang-format (formatting) + clang-tidy (static analysis), per the chosen options.
• Reformat strategy: all C/H sources were reformatted (~920 lines across 31 files) so the new --Werror check is green from the start rather than failing on pre-existing inconsistencies.
• Compile DB: bear -- make is used (one extra apt package in CI) for accurate Zend/PHP include resolution under clang-tidy.

Verification

• clang-format --dry-run --Werror over all .c/.h files → exit 0 (clean).
• .clang-tidy parses cleanly under clang-tidy 19; no unknown check names.
• test:c:format Taskfile command (find/xargs/clang-format dry-run) → exit 0.
• Workflow YAML and Taskfile YAML validated as well-formed.
• Note: full bear -- make + clang-tidy end-to-end run requires PHP headers (not present in the sandbox) and is exercised by CI on ubuntu-latest.

Files

• .clang-format, .clang-tidy (new)
• .github/workflows/test.yml (new lint-c job)
• Taskfile.yml (new C lint/format tasks)
• .gitignore (ignore compile_commands.json)
• All .c/.h sources reformatted (no logic changes)