feat: extension range definition

[MichaelScofield]

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What's changed and what's your intention?

Add our enterprise feature "extension range" traits and hook points etc.

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 PR introduces the "extension range" enterprise feature by adding new traits, hook points, and conditional logic to support extension range scanning and error handling adjustments.

• Adds enterprise-specific extension range traits and integration across scanning, engine, and datanode modules.
• Refactors error handling to use a unified Unexpected error type while conditionally enabling enterprise features.
• Introduces async changes and minor refactoring across scan and range modules.

Reviewed Changes

Copilot reviewed 18 out of 18 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/mito2/src/worker/handle_catchup.rs	Updated error handling for replay entries using UnexpectedSnafu.
src/mito2/src/test_util.rs	Added enterprise-specific conditional parameter.
src/mito2/src/request.rs	Changed error construction for impure default values.
src/mito2/src/read/unordered_scan.rs	Introduced async helper to build scan streams for different range indices.
src/mito2/src/read/series_scan.rs	Adjusted async method chaining for enterprise feature consistency.
src/mito2/src/read/seq_scan.rs	Updated build_sources to an async function with improved error handling.
src/mito2/src/read/scan_util.rs	Refactored async file scan flow; potential issue in metric merging invocation.
src/mito2/src/read/scan_region.rs	Integrated extension range provider logic into the scan region flow.
src/mito2/src/read/range.rs	Added enterprise extension range pushes (noted duplicate calls).
src/mito2/src/read/plain_batch.rs	Unified error handling for default value issues.
src/mito2/src/lib.rs	Introduced the new extension module.
src/mito2/src/extension.rs	Added enterprise extension range traits and provider definitions.
src/mito2/src/error.rs	Refactored legacy error variants to a unified Unexpected type and added enterprise errors.
src/mito2/src/engine/catchup_test.rs	Updated test assertions for error type adjustments.
src/mito2/src/engine.rs	Integrated extension range provider factory in engine construction and scanning.
src/mito2/Cargo.toml	Added enterprise feature flag dependency.
src/datanode/src/datanode.rs	Expanded datanode builder to include enterprise extension range support.
Cargo.toml	Added dependency on cfg-if.

[MichaelScofield]

@evenyag PTAL

[MichaelScofield]

@evenyag PTAL

[fengjiachun]

LGTM