Remove reqwest/tower from default OTLP graph

[lovasoa]

Summary

• disable opentelemetry-otlp default features and keep only OTLP HTTP + metrics with hyper client
• remove reqwest and tower from the default-feature dependency graph
• switch OTLP span/metric export processors to tokio async-runtime variants so hyper OTLP export works reliably

Validation

• cargo fmt --all
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test uploads::test_file_upload_too_large
• cargo tree --no-default-features -i reqwest (no match)
• cargo tree --no-default-features -i tower (no match)

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[chatgpt-codex-connector]

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