Implement HPEXPIRETIME command

[kelvinmwinuka]

Returns the absolute Unix timestamp in milliseconds since Unix epoch at which the given key's field(s) will expire.
Reference: https://redis.io/docs/latest/commands/hpexpiretime/

Client-Server Spec:

Command File: ./internal/modules/hash/commands.go
Test File: ./internal/modules/hash/commands_test.go

Command: hpexpiretime
Module: constants.HashModule
Categories: contants.HashCategory, constants.ReadCategory, constants.FastCategory
Description: (HPEXPIRETIME key FIELDS numfields field [field ...]) Returns the absolute Unix timestamp in milliseconds since Unix epoch at which the given key's field(s) will expire.
Sync: false

NOTE: You may need to change the internal representation of the hash to hold a more complex data type that includes the field's value and expiry time instead of just the value. If the representation is already changed from a previous implementation, use the current one.

Embedded Spec:

Command File: ./echovault/api_hash.go
Test File: ./echovault/api_hash_test.go

Documentation

Add documentation to ./docs/docs/commands/hash/HPEXPIRETIME.mdx