fix: log watched file changes at debug level

[ousamabenyounes]

Fixes #1443.

Changes

• Logs each accepted watcher event at debug level with the changed file path.
• Includes the associated path when the watcher reports one.
• Keeps the existing reload behavior unchanged.

Test verification (RED -> GREEN)

RED on origin/main plus the new regression test before the implementation:

--- FAIL: TestAcceptedEventLogsChangedPathAtDebugLevel (0.00s)
    pattern_test.go:381:
        Error:       "" does not contain "/path/file.php"
        Test:        TestAcceptedEventLogsChangedPathAtDebugLevel
FAIL
FAIL    github.com/dunglas/frankenphp/internal/watcher    0.005s

GREEN after the fix:

ok      github.com/dunglas/frankenphp/internal/watcher    0.008s

Command used for GREEN: go test ./internal/watcher -count=1 in Docker with the watcher C library installed.

[ousamabenyounes]

Thanks for the review. Addressed the feedback in 07c74a4 by removing the extra log-message/attribute constants and keeping the debug log labels inline with the surrounding style.

Validation: local ./run-ci.sh passed for go test ./internal/watcher -count=1 in Docker with the watcher C library built, and the GitHub check rollup for 07c74a4 is green.