fix(admin_audit): handle audit reads for new files

[joshtrichards]

• Resolves: #

Summary

Handle audit logging for file reads that occur before a new file has been assigned a file ID.

BeforeNodeReadEvent can provide a NonExistingFile without an ID. Although #47071 avoided calling getId() for this case, Action::log() still treated the resulting parameter as missing because it used !isset(). As a result, the intended audit entry was not written.

• Follows up on fix(admin_audit): Do not log errors for new files #47071
• Related to the historical behavior addressed by Don't try to generate logs for chunking paths #5185

Changes:

• Use not-yet-assigned as the audit ID for NonExistingFile reads.
• Treat explicitly provided null values as valid audit parameters.
• Clarify Action::log() parameter validation and formatting.
• Support both DateTime and DateTimeImmutable through DateTimeInterface.
• Contraint onAction::log() with PHPDoc to values that can be safely normalized and passed to vsprintf() without introducing a behavior change (static analysis only).
• Avoid repeated node and source/target accessor calls in file actions as a small clarity and performance cleanup.

This preserves the audit event and makes the unavailable ID explicit in the log output:

File with id "not-yet-assigned" accessed: "..."

TODO

• ...

Checklist

• Code is properly formatted
• Sign-off message is added to all commits
• Tests (unit, integration, api and/or acceptance) are included
• Screenshots before/after for front-end changes
• Documentation (manuals or wiki) has been updated or is not required
• Backports requested where applicable (ex: critical bugfixes)
• Labels added where applicable (ex: bug/enhancement, 3. to review, feature component)
• Milestone added for target branch/version (ex: 32.x for stable32)

AI (if applicable)

• The content of this PR was partly or fully generated using AI