Create `SnowflakeIdStr` for stringified Snowflake ID

[rayokamoto]

Can we make a new SnowflakeId type that is "Javascript safe" for the strs that represent a SnowflakeId but a string since Javascript is cringe and can't support 64 bit ints properly?

Something like SnowflakeIdStr

Originally posted by @rayokamoto in #33 (review)