Rework rate manager to use param manager and add tests

[mkysel]

Rework rate management by modifying blockchain.RatesAdmin to use blockchain.ParameterAdmin for writing rate parameters and add tests across pkg/blockchain.

• Update RatesAdmin to depend on a pre-built ParameterAdmin, change blockchain.NewRatesAdmin signature, and refactor RatesAdmin.AddRates to batch-set parameters via ParameterAdmin before invoking the on-chain rates update in rates_admin.go.
• Add uint64 get/set and batch parameter APIs, introduce broadcaster-specific keys, and reorganize parameter constants in parameterAdmin.go.
• Adjust CLI setup to construct ParameterAdmin and pass it to NewRatesAdmin in main.go and rate_registry.go.
• Switch pause status keys to broadcaster-specific variants in appchainAdmin.go.
• Add and update tests for rates admin, parameter admin (including batch flows), and pause keys in rates_admin_test.go, parameterAdmin_test.go, and appchainAdmin_test.go.

📍Where to Start

Start with the constructor blockchain.NewRatesAdmin and the method blockchain.RatesAdmin.AddRates in rates_admin.go.

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Macroscope summarized 2131512.

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