feat: support configurable Quent telemetry exporters

[johanpel]

Summary

Add configurable Quent telemetry exporters and use postcard for the default TPC-H benchmark configuration.

Changes

• Add sirius.telemetry.exporter configuration support for ndjson, msgpack, and postcard.
• Configure the TPC-H benchmark telemetry YAML to use postcard.
• Update Quent to upstream commit 2a5ca834, which includes typed exporter options from feat(codegen): add typed exporter options to bindings rapidsai/quent#499.
• Update Sirius’ Quent analyzer integration for upstream API changes.
• Add pnpm to the Pixi environment, required to build the Quent UI.
• Document exporter configuration and postcard usage for CI and benchmark runs.

Testing

• pixi run make release
• pixi run cargo check --manifest-path rust/Cargo.toml
• pixi run cargo fmt --all --manifest-path rust/Cargo.toml --check
• pixi run build/release/extension/sirius/test/cpp/sirius_unittest "[telemetry_context]"
• Ran TPC-H SF1 query 18 with exporter: postcard.
• Opened the resulting telemetry with the Quent UI and verified it loads successfully.