feat(query): add runtime provider interface

[discord9]

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Refer to a related PR or issue link (optional)

• Enterprise consumer draft PR: https://github.com/GreptimeTeam/greptimedb-enterprise/pull/755

What's changed and what's your intention?

This PR adds a neutral query runtime provider interface for DataFusion session and runtime setup.

Changes included:

• Add QueryRuntimeProvider, QueryRuntimeProviderRef, and QueryRuntimeContext in the query engine.
• Add DefaultQueryRuntimeProvider, which prepares the default RuntimeEnvBuilder and preserves the current runtime environment construction behavior.
• Resolve a provider from Plugins in QueryEngineState::new(), falling back to the default provider when none is registered.
• Allow the provider to configure SessionConfig before SessionState is created.
• Pass the default RuntimeEnvBuilder into the provider so custom providers can preserve existing default setup and append their own runtime customizations.
• Add focused unit tests for default behavior and plugin-provided provider behavior.

Compatibility:

• No user-facing configuration changes.
• No example config, generated config docs, or product docs changes.
• Default behavior remains unchanged when no provider is registered.
• No persisted format, schema, or wire format changes are introduced.

Validation run locally:

• cargo fmt -p query
• cargo test -p query query_runtime_
• cargo check -p query
• cargo clippy -p query --lib --tests -- -D warnings
• git diff --check

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.

[gemini-code-assist]

Code Review

This pull request introduces a new QueryRuntimeProvider trait and its default implementation DefaultQueryRuntimeProvider to decouple and customize the DataFusion session configuration and runtime environment setup in the query engine. It integrates this provider into QueryEngineState by fetching it from plugins, and adds comprehensive unit tests. The review feedback focuses on improving error handling and code ergonomics by: 1) deriving Clone and Copy for QueryRuntimeContext to allow easy reuse, 2) changing the build_runtime_env method in the QueryRuntimeProvider trait to return a Result instead of panicking, and propagating errors using the ? operator across the default provider, state initialization, and test implementations, and 3) reusing a single QueryRuntimeContext instance in QueryEngineState instead of reconstructing it.

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