Simplify json-rpc client handling

[StephenButtolph]

Why this should be merged

Resolves #4056

How this works

This PR:

1. Removes the various Client interfaces, instead exposing the structs directly.
2. Additionally, the Requester is exported, so Clients can be constructed with custom Requesters.

How this was tested

CI

Need to be documented in RELEASES.md?

No.

[Copilot]

Pull Request Overview

This PR removes previous Client interfaces in favor of concrete client structs, exposes the underlying Requester for custom RPC implementations, and updates method signatures across various wallets and VM packages to use pointer receivers.

• Exposed Requester on client structs for custom RPC requesters
• Converted many Client methods and constructors to pointer receivers
• Removed redundant interface definitions and unified client code structure

Reviewed Changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
wallet/subnet/primary/api.go	Switched UTXO client assignments and pointer types
wallet/chain/*	Updated client parameters to pointer types
vms/platformvm/client.go	Removed interface, added concrete Client with Requester
vms/avm/*.go	Removed interfaces, switched to exported structs with Requester
vms/example/xsvm/api/client.go	Switched to concrete Client struct and pointer receiver
indexer/client.go	Removed interface, added concrete Client struct
api/*/client.go	Removed interface, added concrete Client with Requester
tests/*	Updated tests to use new pointer-based client types

Comments suppressed due to low confidence (8)

vms/platformvm/client.go:32

• Add a doc comment for the exported NewClient function, e.g., // NewClient returns a new P-chain Client configured to the given endpoint URI.

func NewClient(uri string) *Client {

indexer/client.go:26

• Add a doc comment for the exported NewClient function, e.g., // NewClient creates an indexer client for the given endpoint URI.

func NewClient(uri string) *Client {

api/info/client.go:21

• Add a doc comment for the exported NewClient function, e.g., // NewClient returns an Info API client pointed at the given URI.

func NewClient(uri string) *Client {

api/health/client.go:17

• Add a doc comment for the exported NewClient function, e.g., // NewClient returns a Health API client configured to the given URI.

func NewClient(uri string) *Client {

api/admin/client.go:21

• Add a doc comment for the exported NewClient function, e.g., // NewClient returns an Admin API client for the given URI.

func NewClient(uri string) *Client {

vms/avm/client.go:28

• Add a doc comment for the exported NewClient function, e.g., // NewClient returns an X-Chain client for the specified URI and chain alias.

func NewClient(uri, chain string) *Client {

vms/example/xsvm/api/client.go:22

• Add a doc comment for the exported NewClient function, e.g., // NewClient returns an xsvm API client for the given URI and chain ID.

func NewClient(uri, chain string) *Client {

vms/avm/wallet_client.go:30

• Add a doc comment for the exported NewWalletClient function, e.g., // NewWalletClient returns a wallet client for the specified AVM chain.

func NewWalletClient(uri, chain string) *WalletClient {