Add archiving metrics code with timer

[caddoo]

Description

Adds a simple timing class for archiving context, recording results in this format:

archiving_metrics
├─ metadataid             BIGINT UNSIGNED PK AUTO_INCREMENT
├─ idarchive              BIGINT UNSIGNED NULL (idx: idx_archiving_metrics_idarchive)
├─ idsite                 INTEGER UNSIGNED NOT NULL
├─ segment                VARCHAR(255) NULL
├─ date1                  DATE NOT NULL
├─ date2                  DATE NOT NULL
├─ period                 VARCHAR(10) NOT NULL (idx: idx_archiving_metrics_site_date_period on idsite, date1, period)
├─ ts_started             DATETIME NOT NULL
├─ ts_finished            DATETIME NOT NULL
├─ total_time             BIGINT UNSIGNED NOT NULL
└─ total_time_exclusive   BIGINT UNSIGNED NOT NULL

Follow up will be integrating with the archiving process
and then a cleanup scheduled task to remove old data.

Checklist

• [✔] I have understood, reviewed, and tested all AI outputs before use
• [✔] All AI instructions respect security, IP, and privacy rules

Review

• Functional review done
• Potential edge cases thought about (behaviour of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• Security review done
• Wording review done
• Code review done
• Tests were added if useful/possible
• Reviewed for breaking changes
• Developer changelog updated if needed
• New documentation added or existing documentation updated

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