fix(deps): pin bitreq 0.3.4 and cover idle keep-alive socket recovery

[storopoli]

Description

Require bitreq 0.3.4 and add a regression test covering the issue #101 scenario where a pooled keep-alive socket is later closed by the server.

The intent here is to avoid carrying a local BitreqClient reset workaround in this crate and instead:

• rely on the recovery behavior observed in bitreq 0.3.4
• lock that minimum version in Cargo.toml
• keep a regression test for the rpcservertimeout-style idle socket close case

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature/Enhancement (non-breaking change which adds functionality or enhances an existing one)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactor
• New or updated tests
• Dependency Update

Notes to Reviewers

This PR intentionally does not add a local pool-reset workaround.

I checked the reported issue scenario against bitreq 0.3.4 and could not reproduce the permanent poisoned-pool behavior described in #101. The new test keeps a connection alive long enough to be pooled, then closes it server-side and verifies the next RPC still succeeds.

This also keeps us aligned with the upstream direction in rust-bitcoin/corepc#564 rather than adding extra client-side complexity here.

Checklist

• I have performed a self-review of my code.
• I have commented my code where necessary.
• I have updated the documentation if needed.
• My changes do not introduce new warnings.
• I have added tests that prove my changes are effective or that my feature works.
• New and existing tests pass with my changes.

Related Issues

Related to #101. rust-bitcoin/corepc#564 with a bitreq published version bump here would be the one to fix #101.