Perf/clarity contract cache

[cylewitruk-stacks]

Description

Builds on stacks-network#7049 (ResidentBytes impl) for calculating resident memory size.

Adds a size-weighted read-through TinyUFO cache (written by Cloudflare; uses S3-FIFO eviction + TinyLFU admission) for parsed Clarity Contract instances:

• The cache uses a CACHE_WEIGHT_UNIT of 256, which the resident_bytes() size of a CachedContract is divided by (since TinyUFO's weight system uses u16), allowing for a maximum cacheable entry size of roughly 16MiB each.
• The DEFAULT_CONTRACT_CACHE_SIZE is set to 64MiB (64 * 1024 * 1024), which gives a cache-wide weight limit of 262,144 units. TinyUFO enforces this budget on every insertion, evicting entries by access frequency to stay within the limit.
• The cache tracks the last block hash + epoch and clears itself when it detects a reorg or epoch change to prevent providing stale contracts.
• Read-only/ephemeral Clarity db's are wired up, but will only use the cache if reading at chain tip.

Applicable issues

• Part of https://github.com/stx-labs/core-epics/issues/126

Additional info (benefits, drawbacks, caveats)

NOTE: The cache is implemented as a node-level cache and as such is purely a node optimization; a next iteration which incorporates tx-level caching policy for targeting tenure budgets could implement its own tx-scoped cache on top of the node-level cache with stricter/deterministic policy.

Some benchmark results:

Benchmark	No Cache	Cached	Speedup
direct_call/increment	32.456 µs	8.248 µs	3.9x
contract_call/proxy_increment	55.053 µs	9.462 µs	5.8x
repeated_calls/10x_proxy_increment	799.16 µs	119.73 µs	6.7x
deep_fold/4_deep_x20_fold	2,150.6 µs	255.66 µs	8.4x

Checklist

• Test coverage for new or modified code paths
• Changelog fragment(s) or "no changelog" label added (see changelog.d/README.md)