Fix AsyncJsonRpcClient to reuse HttpClient

[grawert]

High Level Overview of Change

• Simple fix for AsyncJsonRpcClient to reuse the HttpClient connection

Context of Change

AsyncJsonRpcClient is creating a new HttpClient for each request. The fix makes AsyncJsonRpcClient reuse the client connection.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactor (non-breaking change that only restructures code)
• Tests (You added tests for code that already exists, or your new feature included in this PR)
• Documentation Updates
• Release

Before / After

2025-06-19T15:08:48.013111Z  INFO xrp_app: Call 0: Account balance: 1.99975 XRP
2025-06-19T15:08:48.027369Z DEBUG get_account_balance: reqwest::connect: starting new connection: https://s.altnet.rippletest.net:51234/ 
2025-06-19T15:08:48.028163Z DEBUG get_account_balance: hyper_util::client::legacy::connect::http: connecting to 35.171.235.228:51234
2025-06-19T15:08:48.144391Z DEBUG get_account_balance: hyper_util::client::legacy::connect::http: connected to 35.171.235.228:51234
2025-06-19T15:08:48.538461Z DEBUG hyper_util::client::legacy::pool: pooling idle connection for ("https", s.altnet.rippletest.net:51234)
2025-06-19T15:08:48.538618Z  INFO xrp_app: Call 1: Account balance: 1.99975 XRP
2025-06-19T15:08:48.551663Z DEBUG get_account_balance: reqwest::connect: starting new connection: https://s.altnet.rippletest.net:51234/ 
2025-06-19T15:08:48.552626Z DEBUG get_account_balance: hyper_util::client::legacy::connect::http: connecting to 35.171.235.228:51234
2025-06-19T15:08:48.668859Z DEBUG get_account_balance: hyper_util::client::legacy::connect::http: connected to 35.171.235.228:51234
2025-06-19T15:08:49.061919Z DEBUG hyper_util::client::legacy::pool: pooling idle connection for ("https", s.altnet.rippletest.net:51234)
2025-06-19T15:08:49.062203Z  INFO xrp_app: Call 2: Account balance: 1.99975 XRP
2025-06-19T15:08:49.076024Z DEBUG get_account_balance: reqwest::connect: starting new connection: https://s.altnet.rippletest.net:51234/ 
2025-06-19T15:08:49.076678Z DEBUG get_account_balance: hyper_util::client::legacy::connect::http: connecting to 35.171.235.228:51234
2025-06-19T15:08:49.192298Z DEBUG get_account_balance: hyper_util::client::legacy::connect::http: connected to 35.171.235.228:51234
2025-06-19T15:08:49.585268Z DEBUG hyper_util::client::legacy::pool: pooling idle connection for ("https", s.altnet.rippletest.net:51234)
2025-06-19T15:08:49.585566Z  INFO xrp_app: Call 3: Account balance: 1.99975 XRP
2025-06-19T15:08:49.598022Z DEBUG get_account_balance: reqwest::connect: starting new connection: https://s.altnet.rippletest.net:51234/ 
2025-06-19T15:08:49.599128Z DEBUG get_account_balance: hyper_util::client::legacy::connect::http: connecting to 35.171.235.228:51234
2025-06-19T15:08:49.714901Z DEBUG get_account_balance: hyper_util::client::legacy::connect::http: connected to 35.171.235.228:51234
2025-06-19T15:08:50.106887Z DEBUG hyper_util::client::legacy::pool: pooling idle connection for ("https", s.altnet.rippletest.net:51234)
2025-06-19T15:08:50.107174Z  INFO xrp_app: Call 4: Account balance: 1.99975 XRP
2025-06-19T15:08:50.119358Z DEBUG get_account_next_valid_sequence: reqwest::connect: starting new connection: https://s.altnet.rippletest.net:51234/
2025-06-19T15:08:50.120389Z DEBUG get_account_next_valid_sequence: hyper_util::client::legacy::connect::http: connecting to 35.171.235.228:51234
2025-06-19T15:08:50.239872Z DEBUG get_account_next_valid_sequence: hyper_util::client::legacy::connect::http: connected to 35.171.235.228:51234
2025-06-19T15:08:50.634226Z DEBUG hyper_util::client::legacy::pool: pooling idle connection for ("https", s.altnet.rippletest.net:51234)

After patch applied:

2025-06-19T15:11:35.204603Z  INFO xrp_app: Call 0: Account balance: 1.99975 XRP       
2025-06-19T15:11:35.204858Z DEBUG get_account_balance: hyper_util::client::legacy::pool: reuse idle connection for ("https", s.altnet.rippletest.net:51234)
2025-06-19T15:11:35.480795Z DEBUG hyper_util::client::legacy::pool: pooling idle connection for ("https", s.altnet.rippletest.net:51234)2025-06-19T15:11:35.481047Z  INFO xrp_app: Call 1: Account balance: 1.99975 XRP   
2025-06-19T15:11:35.481201Z DEBUG get_account_balance: hyper_util::client::legacy::pool: reuse idle connection for ("https", s.altnet.rippletest.net:51234)
2025-06-19T15:11:35.604840Z DEBUG hyper_util::client::legacy::pool: pooling idle connection for ("https", s.altnet.rippletest.net:51234)
2025-06-19T15:11:35.605091Z  INFO xrp_app: Call 2: Account balance: 1.99975 XRP   
2025-06-19T15:11:35.605243Z DEBUG get_account_balance: hyper_util::client::legacy::pool: reuse idle connection for ("https", s.altnet.rippletest.net:51234)
2025-06-19T15:11:35.878113Z DEBUG hyper_util::client::legacy::pool: pooling idle connection for ("https", s.altnet.rippletest.net:51234)2025-06-19T15:11:35.878331Z  INFO xrp_app: Call 3: Account balance: 1.99975 XRP   
2025-06-19T15:11:35.878548Z DEBUG get_account_balance: hyper_util::client::legacy::pool: reuse idle connection for ("https", s.altnet.rippletest.net:51234)
2025-06-19T15:11:36.152513Z DEBUG hyper_util::client::legacy::pool: pooling idle connection for ("https", s.altnet.rippletest.net:51234)
2025-06-19T15:11:36.152762Z  INFO xrp_app: Call 4: Account balance: 1.99975 XRP   
2025-06-19T15:11:36.152910Z DEBUG get_account_next_valid_sequence: hyper_util::client::legacy::pool: reuse idle connection for ("https", s.altnet.rippletest.net:51234)
2025-06-19T15:11:36.424893Z DEBUG hyper_util::client::legacy::pool: pooling idle connection for ("https", s.altnet.rippletest.net:51234)

Test Plan

[sephynox]

@grawert You may merge when ready.