store/cachekv: reduce allocation with []byte -> string in map keys (#9275)

Uses internal/conv throughout store/kv which shows performance gains.

Benchmark for store/cachekv:

name                          old time/op    new time/op    delta
CacheKVStoreIterator500-8       23.4µs ± 1%    23.3µs ± 1%     ~     (p=0.095 n=5+5)
CacheKVStoreIterator1000-8      46.7µs ± 1%    46.2µs ± 0%   -0.96%  (p=0.008 n=5+5)
CacheKVStoreIterator10000-8      457µs ± 1%     455µs ± 1%     ~     (p=1.000 n=5+5)
CacheKVStoreIterator50000-8     2.59ms ± 2%    2.47ms ± 1%   -4.64%  (p=0.008 n=5+5)
CacheKVStoreIterator100000-8    7.33ms ± 3%    6.91ms ± 1%   -5.75%  (p=0.008 n=5+5)
CacheKVStoreGetNoKeyFound-8      423ns ± 1%     391ns ± 2%   -7.41%  (p=0.008 n=5+5)
CacheKVStoreGetKeyFound-8        267ns ± 3%     264ns ± 2%     ~     (p=0.595 n=5+5)

name                          old alloc/op   new alloc/op   delta
CacheKVStoreIterator500-8       5.18kB ± 0%    5.18kB ± 0%     ~     (all equal)
CacheKVStoreIterator1000-8      9.29kB ± 0%    9.29kB ± 0%     ~     (p=0.079 n=4+5)
CacheKVStoreIterator10000-8     85.2kB ± 0%    84.9kB ± 0%   -0.30%  (p=0.008 n=5+5)
CacheKVStoreIterator50000-8      468kB ± 1%     458kB ± 0%   -2.17%  (p=0.008 n=5+5)
CacheKVStoreIterator100000-8    1.16MB ± 1%    1.10MB ± 0%   -5.34%  (p=0.008 n=5+5)
CacheKVStoreGetNoKeyFound-8       222B ± 1%      214B ± 0%   -3.78%  (p=0.008 n=5+5)
CacheKVStoreGetKeyFound-8        51.0B ± 0%     51.0B ± 0%     ~     (all equal)

name                          old allocs/op  new allocs/op  delta
CacheKVStoreIterator500-8         13.0 ± 0%      13.0 ± 0%     ~     (all equal)
CacheKVStoreIterator1000-8        13.0 ± 0%      13.0 ± 0%     ~     (all equal)
CacheKVStoreIterator10000-8       51.0 ± 0%      43.0 ± 0%  -15.69%  (p=0.008 n=5+5)
CacheKVStoreIterator50000-8      1.22k ± 4%     0.94k ± 1%  -23.04%  (p=0.008 n=5+5)
CacheKVStoreIterator100000-8     6.48k ± 4%     4.85k ± 1%  -25.12%  (p=0.008 n=5+5)
CacheKVStoreGetNoKeyFound-8       5.00 ± 0%      4.00 ± 0%  -20.00%  (p=0.008 n=5+5)
CacheKVStoreGetKeyFound-8         2.00 ± 0%      2.00 ± 0%     ~     (all equal)

Benchmark for x/auth/keeper:

name                            old time/op    new time/op    delta
AccountMapperGetAccountFound-8    1.27µs ± 3%    1.26µs ± 1%    ~     (p=0.270 n=5+5)
AccountMapperSetAccount-8         3.53µs ± 0%    3.44µs ± 1%  -2.59%  (p=0.008 n=5+5)

name                            old alloc/op   new alloc/op   delta
AccountMapperGetAccountFound-8      440B ± 0%      440B ± 0%    ~     (all equal)
AccountMapperSetAccount-8         2.13kB ± 0%    2.08kB ± 0%  -2.31%  (p=0.008 n=5+5)

name                            old allocs/op  new allocs/op  delta
AccountMapperGetAccountFound-8      10.0 ± 0%      10.0 ± 0%    ~     (all equal)
AccountMapperSetAccount-8           42.0 ± 0%      38.0 ± 0%  -9.52%  (p=0.008 n=5+5)

Fixes #9274

store/cachekv/store.go

@@ -59,7 +59,7 @@ func (store *Store) Get(key []byte) (value []byte) {
 
 	types.AssertValidKey(key)
 
-	cacheValue, ok := store.cache[string(key)]
+	cacheValue, ok := store.cache[conv.UnsafeBytesToStr(key)]
 	if !ok {
 		value = store.parent.Get(key)
 		store.setCacheValue(key, value, false, false)
@@ -238,12 +238,12 @@ func (store *Store) dirtyItems(start, end []byte) {
 
 // Only entrypoint to mutate store.cache.
 func (store *Store) setCacheValue(key, value []byte, deleted bool, dirty bool) {
-	store.cache[string(key)] = &cValue{
+	store.cache[conv.UnsafeBytesToStr(key)] = &cValue{
 		value:   value,
 		deleted: deleted,
 		dirty:   dirty,
 	}
 	if dirty {
-		store.unsortedCache[string(key)] = struct{}{}
+		store.unsortedCache[conv.UnsafeBytesToStr(key)] = struct{}{}
 	}
 }