chore: add cache hit/miss instrumentation to pagination total cache [Backport release/0.5.z]

[trustify-ci-bot]

Description

Backport of #2443 to release/0.5.z.

Summary by Sourcery

Instrument pagination total cache to record cache hit/miss metrics and backport the change to the release/0.5.z branch.

New Features:

• Add tracing instrumentation for pagination total cache hits and misses.

Chores:

• Backport cache instrumentation changes to the release/0.5.z branch.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

Adds tracing instrumentation and cache hit/miss labeling to the pagination total cache, backporting existing telemetry behavior into the 0.5.z release branch.

Sequence diagram for cached_total cache hit/miss instrumentation

sequenceDiagram
    participant Caller
    participant PaginationCache
    participant Cache
    participant Counter_misses as Counter_misses
    participant TracingSpan as TracingSpan
    participant ComputeFn as compute

    Caller->>PaginationCache: cached_total(key, compute)
    activate PaginationCache
    PaginationCache->>Cache: try_get_with(key, async closure)
    activate Cache
    Note over Cache,PaginationCache: Cache miss path within async closure
    Cache->>Counter_misses: add(1, [])
    Cache->>TracingSpan: record(cache_hit, false)
    Cache->>ComputeFn: compute()
    ComputeFn-->>Cache: total
    Cache-->>PaginationCache: total
    deactivate Cache
    PaginationCache-->>Caller: HttpResponse/Result
    deactivate PaginationCache

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File-Level Changes

Change	Details	Files
Instrument pagination total cache lookups with tracing and explicit cache hit/miss labeling.	Import the tracing::instrument macro to support function-level instrumentation. Annotate PaginationCache::cached_total with an #[instrument] macro that skips self and compute, and predefines a cache_hit field as true. On cache miss, increment the OpenTelemetry miss counter and set the cache_hit span field to false before computing the total.	common/src/db/pagination_cache.rs

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