refactor: encapsulate oracle config access via getter methods

[zargarzadehm]

Closes: #333

• Add getter methods for oracle_address, oracle_mnemonic, change_address, and network_prefix
• Prefer reading oracle_mnemonic from env vars or oracle-config file
• Replace direct field access with getter methods throughout the codebase
• Remove unnecessary address cloning and unwrapping
• Improve encapsulation and enable more secure config handling

Breaking Change:
Oracle operators must now add oracle_network: mainnet to their oracle_config.yaml file.
The oracle_address field is no longer required and can be removed.

Secret Loading Priority:
The application now loads the oracle's secret or mnemonic using the following priority:

1. ORACLE_WALLET_SECRET (hex format) from environment variables
2. oracle_secret from oracle_config.yaml
3. ORACLE_WALLET_MNEMONIC from environment variables
4. oracle_mnemonic from oracle_config.yaml

[coveralls]

Pull Request Test Coverage Report for Build 15366130552

Details

• 6 of 102 (5.88%) changed or added relevant lines in 14 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.6%) to 53.24%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
core/src/cli_commands/prepare_update.rs	2	3	66.67%
core/src/explorer_api.rs	0	1	0.0%
core/src/node_interface/node_api.rs	0	1	0.0%
core/src/pool_commands.rs	0	1	0.0%
core/src/actions.rs	0	2	0.0%
core/src/cli_commands/bootstrap.rs	0	2	0.0%
core/src/metrics.rs	0	2	0.0%
core/src/api.rs	0	3	0.0%
core/src/cli_commands/extract_reward_tokens.rs	0	3	0.0%
core/src/cli_commands/transfer_oracle_token.rs	0	3	0.0%

Totals
Change from base Build 14595237185:	-0.6%
Covered Lines:	2005
Relevant Lines:	3766

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💛 - Coveralls