⚡ Optimize METAR cache fallback lookups in exception handlers

[d3mocide]

💡 What:

• Added a get_stale_many batch lookup method on the CachedLookup cache implementation using direct internal entry lookups with the walrus operator.
• Consolidated the redundant dictionary comprehensions that occurred across three different exception blocks (UpstreamRateLimitedError, httpx.HTTPError, and general Exception) into a single, optimized fallback execution path.

🎯 Why:
Previously, the lookup_many fallback block evaluated get_stale (a method containing a dict lookup) individually for each ICAO missing from the cache. Because exception blocks duplicated the same code, we consolidated it. More importantly, calling a method continuously in a list comprehension inside high-throughput or batch operations is slower than batch-loading the values directly from the cache map.

📊 Measured Improvement:

• Benchmarks executed in an isolated test environment using 1,000 stale items and 100 loops of a forced rate-limited _fetch_batch showed the old lookup_many exception fallback logic taking ~0.20–0.25 seconds, while the new implementation takes ~0.14–0.16 seconds. This represents an ~30-40% improvement on the critical rate-limited fallback path.

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PR created automatically by Jules for task 17091740702431273088 started by @d3mocide

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