fix: Update network nicknames and block explorer URLs

[FrederikBolding]

Explanation

Updates all network nicknames to match overrides used by the clients. Additionally, ensure block explorer URLs are populated by default so the client doesn't have to do it.

References

https://consensyssoftware.atlassian.net/browse/WPC-1051

Checklist

• I've updated the test suite for new or updated code as appropriate
• I've updated documentation (JSDoc, Markdown, etc.) for new or updated code as appropriate
• I've communicated my changes to consumers by updating changelogs for packages I've changed
• I've introduced breaking changes in this PR and have prepared draft pull requests for clients and consumer packages to resolve them

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Note

Low Risk
UI-facing display strings and default network metadata only; no auth, RPC, or transaction logic changes.

Overview
Aligns default built-in network display names with client overrides by updating NetworkNickname in @metamask/controller-utils (e.g. Ethereum Mainnet → Ethereum, BSC Mainnet → BNB Chain, Optimism Mainnet → OP).

NetworkController now seeds default Infura network configurations with block explorer URLs from BUILT_IN_NETWORKS (blockExplorerUrls plus defaultBlockExplorerUrlIndex: 0) instead of leaving them empty, so clients do not need to patch explorers separately.

Changelogs and NetworkController test snapshots/error strings were updated to match the new names and explorer fields.

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[mikesposito]

Current client overrides do not affect the initial state of NetworkController, so AFAIK these names are effectively used on onboarding users.

They are also the same as the client config API: https://client-config.api.cx.metamask.io/v1/config/networks

Not an issue, just something I thought it would be good to point out as it's unclear who should be the source of truth to align to

[FrederikBolding]

Current client overrides do not affect the initial state of NetworkController, so AFAIK these names are effectively used on onboarding users.

They are also the same as the client config API: https://client-config.api.cx.metamask.io/v1/config/networks

Not an issue, just something I thought it would be good to point out as it's unclear who should be the source of truth to align to

The changes here should also only apply to onboarding users, it is simply meant to standardize that across clients and ensure this is the default behaviour.