refactor: convert to prometheus values directly from arrow

[MichaelScofield]

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What's changed and what's your intention?

following #7131
for prometheus values (http output)

also reduced some memory for storing intermediate prometheus series data

PR Checklist

Please convert it to a draft if some of the following conditions are not met.

• I have written the necessary rustdoc comments.
• I have added the necessary unit tests and integration tests.
• This PR requires documentation updates.
• API changes are backward compatible.
• Schema or data changes are backward compatible.

[Copilot]

Pull Request Overview

This pull request introduces a new Column type (a wrapper around Arc<String>) to optimize memory usage in Prometheus HTTP API responses by avoiding unnecessary string cloning when column names are used as HashMap keys.

Key changes:

• Introduced the Column type to hold Arc references to column names
• Refactored record_batches_to_series to use a new RowWriter struct for comprehensive data type handling
• Updated test cases to use the new Column type

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/servers/src/http/prometheus.rs	Introduces Column type, adds RowWriter for row-by-row conversion with comprehensive data type support, implements trait-based column reference pattern for efficient HashMap lookups
tests-integration/tests/http.rs	Updates test to import and use the new Column type in series assertions

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