Implement FT.SPELLCHECK command

[vyavdoshenko]

The FT.SPELLCHECK command is used to perform spelling correction on a given query.
It helps detect misspelled words and suggest possible corrections based on custom dictionaries.

FT.SPELLCHECK index query [DISTANCE distance] [TERMS INCLUDE|EXCLUDE dictionary ...]

Related Commands

FT.SPELLCHECK works with custom dictionaries managed by the following commands:

• FT.DICTADD <term ...> - Adds one or more terms to a dictionary.
• FT.DICTDEL <term ...> - Removes terms from a dictionary.
• FT.DICTDUMP - Returns all terms stored in a dictionary.

These dictionaries act as sources for spellchecking suggestions.