Stake/payment → compute-time pricing

[JSONbored]

Problem: No formula exists tying a customer's payment or stake to an amount of allocated miner compute-time.

Area: gittensor economics

Proposal: Implement the pricing mechanism defined by #4781 as a configurable formula/table (not a hardcoded one-off), so pricing can be adjusted without a code change.

Deliverables:

• A working conversion from payment/stake amount to allocated compute-time, configurable rather than hardcoded.

Acceptance criteria:

• Changing the price/rate does not require a code deployment.

Boundaries:

• Blocked on gittensor rental economics spec #4781.
• Actual rate/price figures are a business decision made in Pricing model & rate card #4804, not invented in this engineering issue.

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Part of #4778.

[linear-code]

JSO-3462