feat(gas_price_service): update block committer da source with established contract

[rymnc]

[!NOTE] This is PR 7/7 for https://github.com/FuelLabs/fuel-core/issues/2139

Linked Issues/PRs

• https://github.com/FuelLabs/fuel-core/issues/2139

Description

Updates the BlockCommitterApi to implement the contract established with us and the block committer team. There is some business logic that is slightly unclear, need @MitchTurner for insights.

Checklist

• [x] Breaking changes are clearly marked as such in the PR description and changelog
• [x] New behavior is reflected in tests
• [x] The specification matches the implemented behavior (link update PR if changes are needed)

Before requesting review

• [x] I have reviewed the code myself
• [ ] I have created follow-up issues caused by this PR and linked them here

After merging, notify other teams

[Add or remove entries as needed]

• [ ] Rust SDK
• [ ] Sway compiler
• [ ] Platform documentation (for out-of-organization contributors, the person merging the PR will do this)
• [ ] Someone else?