feat: use simplified configuration management

[bmuddha]

Summary by CodeRabbit

• Refactor

  • Unified configuration into a layered model (CLI > Env > TOML > Defaults); renamed and standardized config keys (accountsdb, database-size, index-size, block-time) and simplified ledger reset behavior.

• New Features

  • Added ValidatorParams, new CLI options (listen, metrics), structured remote endpoints, Loadable programs list, new config types (ledger, accountsdb, chainlink, metrics), plus an example config and README.

• Removed

  • Removed legacy macro-based helpers, old EphemeralConfig surface, obsolete config modules and many legacy fixtures/tests.

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