improve: implement a common interface in sdk providers

[bmzig]

Ideally we can make custom implementations for our providers (e.g. speedProvider) and also make providers for other networks (e.g. a Solana provider) while still using a common utility type (e.g. BlockFinder). I think a good way to achieve this is to extend these providers from a common interface and start utilizing generic types more.

[bmzig]

Unsafe cast here. Marking as need to change.

[pxrl]

getTransactionCount is another one that seems to be common.

[pxrl]

This could be simplified by narrowing the string type.

Suggested change

	async getBlock(blockNumber: string | number): Promise<unknown> {
	// TODO: Support other evm block tags.
	let slot;
	try {
	slot = BigInt(blockNumber);
	} catch {
	// Assume block tag = "latest";
	slot = BigInt(await this.getBlockNumber());
	}
	return this.rateLimitedRpcClient.getBlock(slot, {});
	}
	async getBlock(blockNumber: number | "latest"): Promise<unknown> {
	const slot = blockNumber === "latest"
	? BigInt(await this.getBlockNumber())
	: BigInt(blockNumber);
	return this.rateLimitedRpcClient.getBlock(slot, {});
	}