mev_sendBundle privacy.hints default behavior

[This spec](https://docs.flashbots.net/flashbots-mev-share/searchers/understanding-bundles#bundle-definition) doesn't specify the default behavior for privacy.hints. If the `privacy` field is missing, or if `privacy.hints` is missing, what information is shared to the public MEVShare feed? This should be explicit.

Start with the linked Bundle Definition specification and review the surrounding mev_sendBundle privacy documentation. Determine the behavior when privacy or privacy.hints is omitted, then document that default explicitly and verify the wording is consistent with the specification.

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