feat: add hstrlen command for hash

[rfyiamcool]

summary

Add HSTRLEN command for HASH.

https://redis.io/commands/hstrlen/

[ofekshenawa]

Maybe changing the type of field to interface{}?
To enhance flexibility by supporting multiple data types and simplifying API usage across different caller scenario.
WDYT?

[rfyiamcool]

I found type of field in hash commands is string type, so I need to be consistent with the other hash commands ? 😁

// hash_commands.go:5
type HashCmdable interface {
	HDel(ctx context.Context, key string, fields ...string) *IntCmd
	HExists(ctx context.Context, key, field string) *BoolCmd
	HGet(ctx context.Context, key, field string) *StringCmd
	HIncrBy(ctx context.Context, key, field string, incr int64) *IntCmd
	HIncrByFloat(ctx context.Context, key, field string, incr float64) *FloatCmd
	HMGet(ctx context.Context, key string, fields ...string) *SliceCmd
	HSet(ctx context.Context, key string, values ...interface{}) *IntCmd
	HMSet(ctx context.Context, key string, values ...interface{}) *BoolCmd
	HSetNX(ctx context.Context, key, field string, value interface{}) *BoolCmd
	HScan(ctx context.Context, key string, cursor uint64, match string, count int64) *ScanCmd
	HVals(ctx context.Context, key string) *StringSliceCmd
	HRandField(ctx context.Context, key string, count int) *StringSliceCmd
	HRandFieldWithValues(ctx context.Context, key string, count int) *KeyValueSliceCmd
	HStrLen(ctx context.Context, key, field string) *IntCmd
}