Make gas sanitization median based

[Siegrift]

On today's Airseeker call, we talked about:

• Gas scaling using the latest gas price instead of sanitized one. When we sanitize and scale in short succession, we often end up overpaying.
• Current (percentile based) sanitization can suffer if last few minutes cause a gas spike.
• Sanitization could be based on the median of gas prices and multiplied by some factor and also cap the scaling.

The median could be parametrised, but in practice we will likely use only the median. There might be some edge cases, so this should be thought through a bit more. Even if the idea is sounds, it's best to see this work in practice.

[Siegrift]

Specifics: https://api3workspace.slack.com/archives/C05TQPT7PNJ/p1712663616578319

Also update the spec.