refactor list splits pagination, env var to skip initial seeding

[mattmkim]

Description

• we were paginating list metrics/sketch splits with 3 different implementations, puts it in one place
• adds env var to skip intial seeding/fetching of immature splits on startup. TODO is to rewrite the query to only fetch splits we should care about (given some node_id, within the maturity period)

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[chatgpt-codex-connector]

💡 Codex Review

https://github.com/quickwit-oss/quickwit/blob/8a348274c5409a6aaf0804a2d630208a31ac4685/quickwit-indexing/src/actors/metrics_pipeline/mod.rs#L15-L20
Restore the metrics pipeline module declarations

This file now declares metastore submodules such as file_backed, index_metadata, and control_plane_metastore, but the quickwit-indexing/src/actors/metrics_pipeline directory only contains the Parquet pipeline files (parquet_doc_processor.rs, pipeline.rs, etc.; I checked the directory and searched for pub mod file_backed). As soon as the metrics pipeline module is compiled, Rust will look for missing files like metrics_pipeline/file_backed.rs while the real pipeline submodules and re-exports were removed, so metrics indexing cannot build or expose ParquetMergePipeline, MetricsPipeline, and related actors.

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[g-talbot]

Didn't look super deeply but this seems like a worthwhile refactor.

[chatgpt-codex-connector]

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Reviewed commit: 32ecc52f5a

ℹ️ About Codex in GitHub

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• Open a pull request for review
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• Comment "@codex review".

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[chatgpt-codex-connector]

Add the declared compaction metrics module

In the reviewed commit, this new module declaration has no corresponding parquet_compaction_metrics.rs or parquet_compaction_metrics/mod.rs under quickwit-indexing/src/actors/metrics_pipeline (rg --files quickwit/quickwit-indexing/src/actors/metrics_pipeline | rg parquet_compaction_metrics returns nothing). Any build that includes quickwit-indexing will fail with Rust's missing-module error before reaching the pagination changes.

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