web3.js: add sideEffects: false to package.json

[macalinao]

Problem

Adds sideEffects: false to help bundlers tree shake.

[steveluscher]

I would love to be able to do this as part of solana-labs/solana-web3.js#1122, but unfortunately this is not true. We actually do produce side effects on import.

Merely importing PublicKey registers a schema in the global scope.

solana/web3.js/src/publickey.ts

Lines 251 to 254 in 9cb0151

	SOLANA_SCHEMA.set(PublicKey, {
	kind: 'struct',
	fields: [['_bn', 'u256']],
	});

There's a way around this, but it will involve creating new package boundaries – ie. spinning out the side-effectful parts of web3.js into their own packages – but I'm not sure that's worth the lift when I could spend the time on solana-labs/solana-web3.js#1111.