Summary

Closes #2523.

This PR implements the v2 process/transport configuration boundary across SDKs by moving SDK-managed process launch settings off shared client options and onto the out-of-process runtime connection/transport APIs that actually spawn a runtime process.

Current-main findings

Before editing, I refreshed and inspected the latest origin/main and the issue context from #2523, parent #2522, superseded tracker #1934, and linked historical issues/PRs. Current main already contains the compatible in-process groundwork from #1930/#1976 for many first-class options, but the client-wide process launch APIs remained present and could still be configured for transports where they are inapplicable. This PR carries forward the remaining maintainer-intended v2 cleanup from #1934/#2523 rather than treating it as optional design exploration.

Breaking changes and migration

• .NET: removed CopilotClientOptions.WorkingDirectory and CopilotClientOptions.Environment; moved them to stdio/TCP out-of-process runtime connections. Renamed ChildProcessRuntimeConnection to OutOfProcessRuntimeConnection.
• Go: removed ClientOptions.WorkingDirectory and ClientOptions.Env; moved them to StdioConnection and TCPConnection. The unexported child-process helper is renamed to out-of-process terminology.
• Java: removed CopilotClientOptions.cwd/setCwd and CopilotClientOptions.environment/setEnvironment; moved them to StdioRuntimeConnection and TcpRuntimeConnection as workingDirectory and environment. Java has no shared child-process base class, so this intentionally uses the two concrete out-of-process connection types.
• Node.js: removed client-wide workingDirectory and env; moved them to the renamed OutOfProcessRuntimeConnection base used by stdio/TCP connections. Renamed ChildProcessRuntimeConnection accordingly.
• Python: removed client-wide working_directory and env; moved them to the renamed OutOfProcessRuntimeConnection base used by stdio/TCP connections. Renamed ChildProcessRuntimeConnection accordingly.
• Rust: moved program, prefix/raw args, extra_args, working_directory, env, and env_remove from ClientOptions to OutOfProcessOptions carried by the process-spawning transport variants. Transport::External does not expose process launch options because the SDK does not own that process.

The changelog and SDK READMEs include before/after examples for the migration path.

Runtime follow-up

The SDK-side API cleanup is implemented here. Runtime-side per-client host environment consumption remains tracked separately in #2533, the consolidated follow-up for runtime work required by #2523. This PR does not embed or acquire runtime artifacts and does not take lifecycle/SQLite work from #2524/#2525.

Validation

• Refreshed latest origin/main before final rebase.
• Confirmed there are no remaining cross-SDK source references to the removed client-level cwd/environment APIs (getCwd, setCwd, .cwd, CopilotClientOptions.environment, getEnvironment, setEnvironment) after the migration.
• Earlier Java validation during implementation completed ./mvnw test-compile jar:jar, ./mvnw -pl sdk verify -Dskip.test.harness=true, and ./mvnw -pl sdk spotless:check for the environment-only phase. The follow-up cwd/full cross-SDK validation is intentionally left to CI because local E2E/Maven runs were prohibitively expensive in this sandbox.