Enable saving of command keys

[ofekshenawa]

Adds support for extracting and persisting the Redis keys used by each command—particularly multi‐key commands.

Key changes:

• New Keys() method on the Cmder interface, allowing callers to retrieve all keys a command operates on.
• Extended baseCmd to track a keys []string slice and implement Keys() []string.
• Helper for interleaved args: introduced getInterleavedArgumentsWithOffset(offset int) []string to extract key names from commands with key/value pairs (e.g. MSET, MSETNX).
• Command implementations in string_commands.go updated to populate cmd.keys for:
• • Single‐key commands (e.g. GET, SET, INCRBY, APPEND)
• • Multi‐key commands (MGET, MSET, MSETNX)

[vladvildanov]

This approach isn't scalable, each time we need a new type of extracting we have to add a command here. Cmder is an interface that should be abstract as possible and should not contain any implementation specific (mget is an implementation specific in this case).

Cmder should return a keys, but shouldn't be aware about the keys position of specific command (this is implementation details), instead the specific command that implements this interface should define keys position for itself.

[ndyakov]

@vladvildanov , @ofekshenawa should we close this one? Can someone explain what was the need and the plan for this change?

[ofekshenawa]

@vladvildanov , @ofekshenawa should we close this one? Can someone explain what was the need and the plan for this change?

This PR enables saving the keys used by commands—especially multi-key commands—for use in CSC.