dnscache/conncache tweaks

[icing]

• pass more struct curltime pointers around
• as hash keys are now bytes, make the dnscache entry key binary as well, no longer using printf() for formatting
• restrict hostname entry lengths to UINT16_MAX and fail otherwise
• add a permanent bit to entries

[Copilot]

🟡 Changes recommended

Long hostnames can alias cache entries, and negative HTTPS entries no longer receive accelerated expiration.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

Refactors DNS cache keys and timestamps while sharing a single current-time value with connection-cache cleanup.

Changes:

• Uses binary DNS cache keys and explicit permanence state.
• Records cache insertion times and passes time pointers through pruning.
• Updates connection-idle timing and related unit tests.

File summaries

File	Description
tests/unit/unit1607.c	Adapts DNS cache tests to binary keys and permanence.
lib/vdns/dnscache.h	Updates DNS entry fields and pruning API.
lib/vdns/dnscache.c	Implements binary keys, permanence, and insertion timestamps.
lib/multi.c	Shares one timestamp across cleanup operations.
lib/conncache.h	Extends the idle-connection API with a timestamp.
lib/conncache.c	Uses the caller-provided timestamp.

Review details

Suppressed comments (1)

tests/unit/unit1607.c:220

• The assertion now checks dns->permanent, but its failure text still refers to a zero timestamp. Report the permanent flag so the diagnostic matches the failed condition.

      if(dns->permanent && !tests[i].permanent) {

• Files reviewed: 6/6 changed files
• Comments generated: 3
• Review effort level: Balanced

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