refactor: Make makeJsonAgent bundleable with @endo/bundle-source

[grypez]

Refactors kernel-utils and kernel-errors to enable makeJsonAgent to be bundled into vats using @endo/bundle-source.

Changes:

• kernel-utils: Added subpath exports (counter, merge-disjoint-records, schema)
• kernel-errors: Added bundleable subpath with simplified error classes
• kernel-errors: Extracted ErrorCode to error-codes.ts (no @metamask/utils dep)
• ocap-kernel: Moved isRetryableNetworkError from kernel-errors to utils
• kernel-agents: Updated to use subpath imports

The bundler was failing due to transitive dependencies on @noble/hashes (through @metamask/utils) which has ESM/CJS compatibility issues. By using subpath exports and moving libp2p-specific code to ocap-kernel, we avoid pulling in unbundleable dependencies.

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Note

Makes makeJsonAgent bundleable with @endo/bundle-source by isolating unbundleable deps and switching to subpath imports.

• kernel-errors: Extracts ErrorCode to error-codes.ts and adds isSampleGenerationError; introduces bundleable/ with SampleGenerationError and re-exports via ./bundleable; updates BaseError import; removes isRetryableNetworkError from public exports; adds tests.
• kernel-agents: Switches imports to @metamask/kernel-utils/* subpaths and to @metamask/kernel-errors/bundleable; retry logic now uses isSampleGenerationError and SampleGenerationError from bundleable build.
• kernel-utils: Adds subpath exports for counter, merge-disjoint-records, and schema; splits makeCounter into counter.ts and re-exports from misc for backwards compatibility.
• ocap-kernel: Moves isRetryableNetworkError into src/utils/isRetryableNetworkError.ts and updates ConnectionFactory/network to use it.
• Deps/config: Updates package exports and dependencies (e.g., drop @libp2p/interface from kernel-errors, add @metamask/streams/@metamask/utils to kernel-test); lockfile updated.

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