chore: remove dead_code

[de-sh]

Fixes #XXXX.

Description

Quite a few #[allow(dead_code)] lead to stagnant code lying around in the codebase, this cleans that up.

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This PR has:

• been tested to ensure log ingestion and log query works.
• added comments explaining the "why" and the intent of the code wherever would not be obvious for an unfamiliar reader.
• added documentation for new or modified features or behaviors.

[coveralls]

Pull Request Test Coverage Report for Build 12924125300

Details

• 0 of 2 (0.0%) changed or added relevant lines in 1 file are covered.
• 6 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-0.05%) to 12.786%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/event/writer/file_writer.rs	0	2	0.0%

Files with Coverage Reduction	New Missed Lines	%
src/hottier.rs	1	0.0%
src/storage/staging.rs	1	0.0%
src/handlers/http/cluster/utils.rs	2	0.0%
src/handlers/http/logstream.rs	2	1.71%

Totals
Change from base Build 12922515032:	-0.05%
Covered Lines:	2446
Relevant Lines:	19131

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💛 - Coveralls

[nikhilsinhaparseable]

looks good