perf: optimize insert method in Sparse by inlining wordMask logic

[myeunee]

Optimized the insert method in the Sparse type by inlining the logic of the
wordMask function directly within the method. This change eliminates the
overhead of an additional function call, resulting in a slight performance
improvement during insert operations.

While the core logic remains unchanged, this optimization could provide minor
gains in performance, particularly in tight loops or performance-sensitive
scenarios where the insert method is frequently called.

The change has been localized to container/intsets/sparse.go.

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[gopherbot]

Message from Gopher Robot:

Patch Set 1:

(1 comment)

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