Avoid creating expensive Path objects in split creation code

[NikhilCollooru]

Description

Avoid creating expensive Hadoop Path objects in split creation code. Path object creation is cpu intensive.

Motivation and Context

We observed that when coordinator is running hot, a good amount of CPU is being spent on Hadoop Path object creation. So we want to reduce that especially in split creation code path.

Impact

None

Test Plan

unit tests

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[arhimondr]

LGTM % CI