fix: preserve nontransparent live resumption

[he-yufeng]

Summary

Fixes #5675.

BaseLlmFlow.run_live always set session_resumption.transparent = True when reconnecting with a saved live-session handle. That overwrote an explicit transparent=False config, which is the configuration needed for direct Gemini API live-session resumption because GoogleLLM.connect rejects transparent resumption on the Gemini API backend.

This keeps the existing default behavior for reconnects that have no session resumption config yet, but preserves a caller-provided non-transparent config.

Validation

python -m pytest tests/unittests/flows/llm_flows/test_base_llm_flow.py -q
# 29 passed

pyink --check src/google/adk/flows/llm_flows/base_llm_flow.py tests/unittests/flows/llm_flows/test_base_llm_flow.py
isort --check-only src/google/adk/flows/llm_flows/base_llm_flow.py tests/unittests/flows/llm_flows/test_base_llm_flow.py
python -m py_compile src/google/adk/flows/llm_flows/base_llm_flow.py tests/unittests/flows/llm_flows/test_base_llm_flow.py
git diff --check

[rohityan]

Hi @he-yufeng ,Thank you for your contribution! We appreciate you taking the time to submit this pull request. Please fix formatting errors by running autoformat.sh

[he-yufeng]

Rebased onto current upstream/main and re-ran the focused checks locally.

Validation:

PYTHONUTF8=1 .\.venv\Scripts\python.exe -m pytest tests\unittests\flows\llm_flows\test_base_llm_flow.py -q --basetemp .tmp\pytest-5676
# 29 passed, 1 warning

PYTHONUTF8=1 .\.venv\Scripts\python.exe -m pyink src\google\adk\flows\llm_flows\base_llm_flow.py tests\unittests\flows\llm_flows\test_base_llm_flow.py --check
PYTHONUTF8=1 .\.venv\Scripts\python.exe -m py_compile src\google\adk\flows\llm_flows\base_llm_flow.py tests\unittests\flows\llm_flows\test_base_llm_flow.py
git diff --check

The previous failure was the pre-commit formatting check; this branch is now a single commit on current main.

[he-yufeng]

Rebased this onto current main and reran the focused checks.

Validation:

PYTHONUTF8=1 .\.venv\Scripts\python.exe -m pytest tests\unittests\flows\llm_flows\test_base_llm_flow.py -q --basetemp .tmp\pytest-5676-rebase
# 31 passed, 1 warning

PYTHONUTF8=1 .\.venv\Scripts\python.exe -m pyink src\google\adk\flows\llm_flows\base_llm_flow.py tests\unittests\flows\llm_flows\test_base_llm_flow.py --check
PYTHONUTF8=1 .\.venv\Scripts\python.exe -m py_compile src\google\adk\flows\llm_flows\base_llm_flow.py tests\unittests\flows\llm_flows\test_base_llm_flow.py
git diff --check upstream/main..HEAD

[he-yufeng]

Rebased onto current main again; no code changes beyond the rebase.\n\nValidation on Windows:\n- uv run --no-sync pytest tests\unittests\flows\llm_flows\test_base_llm_flow.py -q --basetemp .tmp\pytest-5676-20260524 -p no:cacheprovider -> 31 passed, 1 existing experimental warning\n- uv run --no-sync pyink --check src\google\adk\flows\llm_flows\base_llm_flow.py tests\unittests\flows\llm_flows\test_base_llm_flow.py\n- uv run --no-sync python -m py_compile src\google\adk\flows\llm_flows\base_llm_flow.py tests\unittests\flows\llm_flows\test_base_llm_flow.py\n- git diff --check upstream/main..HEAD