fix(providers): add "nibiru" as chain with chainId 6900 to match ethereum-lists/chains

[Unique-Divine]

Purpose

Adds Nibiru to "providers.json" to accurately propagate its EVM RPC endpoint and chainId of 6900.

Related:

• Aligns with DeFiLlama-Server, which references "nibiru": fix(tokenMappings): Nibiru integrated with LayerZero and Stargate, adding several common ERC20s defillama-server#9893
• Nibiru (eip155-6900): add explorers and fix "shortName" discrepency between DeFiLlama and ethereum-lists/chains ethereum-lists/chains#7329

Rationale

Several TVL Adapters are blocked by "nibiru":

1. missing its chainId field on the ChainApi (api) object,
2. and having the default value of 400069 as the chainId on the LlamaProvider

This can be seen from console logging the api object in the downstream repos.
For example, this is from the uniV3Export helper in the adapters repo:

// DEBUG uniV3Export forEach 
{
  chain: 'nibiru',
  fromBlock: 19674297,
  api: <ref *1> ChainApi {
    block: undefined,
    chain: 'nibiru',
    timestamp: 1747982188,
    provider: LlamaProvider {
      quorum: 1,
      eventQuorum: 1,
      eventWorkers: 1,
      isCustomLlamaProvider: true,
      rpcs: [
        {
          url: 'https://evm-rpc.nibiru.fi',
          provider: JsonRpcProvider {}
        },
        [length]: 1
      ],
      archivalRPCs: [ [length]: 0 ],
      chainName: 'nibiru',
      chainId: 400069,
      _isReady: Promise { undefined },
      [providerConfigs]: [Getter],
      [pollingInterval]: [Getter],
      [provider]: [Getter],
      [plugins]: [Getter],
      [disableCcipRead]: [Getter/Setter],
      [destroyed]: [Getter],
      [paused]: [Getter/Setter]
    },
    _balances: Balances { chain: 'nibiru', timestamp: 1747982188, _balances: {} },
    chainId: undefined,
    storedKey: 'nibiru',
    api: [Circular *1]
  }
}: 

The Point: THe RPC is being picked up from ethereum-lists/chains, but the chainId is not.

[Unique-Divine]

Is there anything else that needs to be edited besides the providers.json file, @g1nt0ki ?