Inline borsh, make is-my-json-valid optional

[mikedotexe]

Toward the goal described in #1876
I've tried to create a couple PRs for ease of review, and this is the first one. It's making some efficiency gains that will be used and leveraged in the two PRs following this. (those have linked to these with decent explanation)

This is the first one that's best to review and consider.

Sidenote, it's interesting that the npm package for borsh is so good it can be serialization for just about anything. What we found here was that it can be much smaller if it's just for the NEAR Protocol side, so that's the idea.

Summary

• Inline borsh serializer — Replace the borsh npm dependency with a lean 289-line zero-dep serializer/deserializer tailored to NEAR's schema needs. Eliminates a transitive dependency tree.
• Make is-my-json-valid optional — Move is-my-json-valid to optionalDependencies and dynamically import it with try/catch fallback. Environments without it still work; ABI schema validation is skipped gracefully.
• Add .claude/ to .gitignore

Changes

File	Change
src/borsh.ts	New — 289-line zero-dep borsh serializer/deserializer
src/transactions/schema.ts	import from 'borsh' → import from '../borsh.js'
src/nep413/schema.ts	import from 'borsh' → import from '../borsh.js'
test/unit/signers/key_pair_signer.test.ts	import from 'borsh' → import from '../../../src/borsh.js'
test/unit/transactions/serialize.test.ts	import from 'borsh' → import from '../../../src/borsh.js'
src/accounts/errors.ts	Inline ValidationError type (was imported from is-my-json-valid)
src/accounts/typed_contract.ts	Dynamic import('is-my-json-valid') with try/catch; validateArguments → async
package.json	Remove borsh from deps; move is-my-json-valid to optionalDependencies

Test plan

• pnpm compile (tsc) — no errors
• pnpm test — all 27 test files, 346 tests pass
• Borsh round-trip coverage: serialize/deserialize for all NEAR transaction types

🤖 Generated with Claude Code

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🦋 Changeset detected

Latest commit: 1d0942f

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
near-api-js	Minor

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[mikedotexe]

will address these failed CI tests 🫡

[mikedotexe]

will address these failed CI tests 🫡

actually, looks like master has CI issues. Thought i'd throw this one-liner PR up, but no worries if it's not the path the team would like to go on: #1897 my thought was just to exclude the e2e side or punt it until later so CI is working on current and incoming PRs

[gagdiez]

Respect to borsh.js

How much does it impact removing borsh?

borsh is already quite small, dependency-free, and thoroughly tested. By inlining it here we would lose not only the tests, but also create redundancy just to save a couple bytes. I would rather not inline it to be honest.

Respect to my-json-valid optional

We might want to consider how useful it actually is, if we can make it optional then maybe we can just delete it? Users that want to use it could simply validate the input by themselves. Because right now we are "silently skipping it", which to me sounds like unexpected behavior more than a feature. cc @denbite