The salvaged fix (#71593) rebuilds Telegram fallback pools lazily and
discards+aclose()s a pool on retryable connect failure (_reset_fallback),
bounding each at Limits(max_connections=8) as a setdefault default. The PR
shipped no test.
Add tests/gateway/test_telegram_fallback_pool_release_71593.py:
* failed fallback pool is aclose()d and dropped from _fallbacks (the
discard-on-failure path — reverting the _reset_fallback call fails it)
* a recovered pool is retained, only the failed one discarded
* _reset_fallback is a no-op when the pool was never built
* caller-supplied limits win over the _POOL_LIMITS setdefault default
* the max_connections=8 default applies when the caller omits limits
Update the eager-build assumptions in test_telegram_network.py to the new
lazy contract (fallbacks materialize via _get_fallback, not in __init__).
