Fixes #13142.

Root cause:
execute_code set HERMES_RPC_DIR only through the remote shell prefix. On Docker, the file-based hermes_tools RPC bridge also needs the RPC directory in the container execution environment; without it, tool calls from inside execute_code could silently resolve to the wrong default and report tool_calls_made: 0.

Fix summary:

• Thread optional per-call extra_env through the execution environment interface.
• Pass HERMES_RPC_DIR as extra_env when running the remote execute_code script, while keeping the existing shell prefix for compatibility.
• Apply extra_env to Docker via docker exec -e KEY=value and to the local backend via the subprocess environment.
• Update other environment backends to accept the optional argument without changing their existing shell-prefix behavior.
• Add regressions proving execute_code passes the RPC dir through extra_env and Docker turns it into docker exec -e HERMES_RPC_DIR=....

Tests:

• uv run --frozen --python 3.11 --extra dev pytest -o addopts= tests/tools/test_code_execution.py tests/tools/test_docker_environment.py -q -> 83 passed, 1 warning
• git diff --check -- tools/code_execution_tool.py tools/environments/base.py tools/environments/docker.py tools/environments/local.py tools/environments/ssh.py tools/environments/modal.py tools/environments/daytona.py tools/environments/singularity.py tests/tools/test_code_execution.py tests/tools/test_docker_environment.py

Note:

• The warning is the existing fake-Popen drain-thread warning in tests/tools/test_docker_environment.py; the targeted suite passed.