[Feature]: Support importing multi-wacz WACZ files

[Shrinks99]

Context

Currently when opening a multi-WACZ file, users are given the error Unexpected Loading Error: TypeError: this.store.loadWACZFiles is not a function. This does not occur when loading regular WACZ files.

Relevant forum thread

What change would you like to see?

Multi-WACZs should load like any other.