Remove the Hashmap from the katz centrality computation

[Paulo-21]

Proposed fix for issue #1173

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[coveralls]

Pull Request Test Coverage Report for Build 8823148065

Details

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• 1 unchanged line in 1 file lost coverage.
• Overall coverage increased (+0.02%) to 96.518%

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Files with Coverage Reduction	New Missed Lines	%
rustworkx-core/src/centrality.rs	1	98.61%
<!--	Total:	1		-->

Totals
Change from base Build 8822969880:	0.02%
Covered Lines:	17325
Relevant Lines:	17950

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💛 - Coveralls