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Fixed cache collisions that could happen when mixing formula and cask operations. Same functionality, just more reliable caching under the hood.

Issue 1: Incomplete Cache Key
The cache was only using the method parameter as the key, ignoring other parameters that affect the result.
Example of the bug:

# First call - caches result with only 'method' as key
method = :some_method
only = :formulae
ignore_unavailable = true
result1 = @to_keys_to_casks[method] ||= # ... computes and caches result

# Second call - WRONG! Returns cached result1 even though parameters differ
method = :some_method        # same
only = :casks               # different!
ignore_unavailable = false  # different!
result2 = @to_keys_to_casks[method]  # incorrectly returns result1

Issue 2: Unsafe Type Assumptions
The partition method splits arrays based on type checking, but makes unsafe assumptions:

# Assume to_formulae_and_casks returns:
[key1, key2, formula1, formula2, some_other_object]

# partition { |o| o.is_a?(Key) } results in:
[
  [key1, key2],                           # Array of Key objects
  [formula1, formula2, some_other_object] # Array of NON-Key objects
]