receiver: oversized trace_id/span_id bytes silently converted

[planetf1]

crates/otelite-receiver/src/conversion.rs:102-150 calls bytes_to_hex() on raw protobuf bytes without length validation. OTLP spec: trace_id is 16 bytes (32 hex), span_id is 8 bytes (16 hex). Oversized inputs produce malformed IDs that may break downstream queries.

Suggested fix: enforce length bounds; reject (or truncate + warn) oversized values.

Acceptance criteria: a fuzz/property test asserts that any bytes input produces either a 32-char trace_id or an explicit error.

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Filed from review on 2026-05-15.