feat: Add --network flag to CLI tools for multi-network support

[rockysingh]

Summary

• Adds a NetworkConfig record with static current() singleton that holds all network-specific parameters (GCS bucket, mirror node URL, genesis date, node range, genesis address book, etc.)
• Adds --network option (mainnet/testnet) to BlockStreamTool root command with scope = ScopeType.INHERIT, making it available on all subcommands
• Replaces hardcoded mainnet values across 16 files with NetworkConfig.current() references
• AddressBookRegistry falls back to fetching the genesis address book from the mirror node API at runtime when a bundled resource isn't available (e.g. for testnet)

Files Changed

Area	Files	Change
New	NetworkConfig.java	Central config record with mainnet() / testnet() factories
CLI root	BlockStreamTool.java	--network option with inherited scope
GCS bucket	DownloadConstants.java, MainNetBucket.java, DownloadDayImplV2.java, LiveDownloader.java	Bucket name + path prefix from NetworkConfig
Mirror node	FetchBlockQuery.java, FixBlockTime.java, BlockTimeCommand.java, UpdateBlockData.java, MirrorNodeAddressBook.java, ExtractDayBlocksFromApi.java	Mirror node URL from NetworkConfig
Genesis date	DownloadDaysV3.java, UpdateDayListingsCommand.java, Validate.java, ValidateWithStats.java	Genesis date + node range from NetworkConfig
Address book	AddressBookRegistry.java	Genesis address book resource from NetworkConfig with mirror node fallback

Test plan

• ./gradlew :tools:compileJava — compiles without errors
• ./gradlew :tools:test — all 1075 existing tests pass
• ./gradlew spotlessApply — formatting clean
• Default behavior unchanged: commands without --network still use mainnet
• Testnet: --network testnet commands hit testnet mirror node and GCS bucket

Closes #2268

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

@@             Coverage Diff              @@
##               main    #2283      +/-   ##
============================================
+ Coverage     80.74%   80.90%   +0.16%     
- Complexity     1461     1463       +2     
============================================
  Files           139      139              
  Lines          6766     6766              
  Branches        728      728              
============================================
+ Hits           5463     5474      +11     
+ Misses          984      969      -15     
- Partials        319      323       +4     

see 2 files with indirect coverage changes

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