TracingService.start_tracers() wraps all 8 tracers in one try/except — one missing optional dependency disables native tracing too

Bug Description

TracingService.start_tracers() initializes all eight supported tracers (the built-in NativeTracer, which has no external dependency, plus seven optional third-party integrations — Langfuse, Langsmith, Arize Phoenix, etc.) inside one shared try/except block. If any single optional third-party dependency is missing — for example Arize Phoenix's openinference package, which isn't installed unless that integration is actually configured — the exception aborts startup for all eight tracers, including the built-in one that needs no external dependency at all and was never configured to use the failing integration.

The observable result: Trace View stays permanently empty, with nothing about native tracing itself broken and no indication that an unrelated, unconfigured integration is what actually killed it.

Reproduction

1. Run Langflow without the optional openinference (Arize Phoenix) package installed, and without configuring Phoenix.
2. Execute any flow.
3. Open Trace View for the run.

Expected: the built-in native trace/span data appears (no external dependency required for NativeTracer). Actual: Trace View is empty. Tracing back through TracingService.start_tracers(), the missing openinference import during Phoenix tracer initialization raises inside the shared try/except and prevents the native tracer (and the other five) from starting at all.

Expected behavior

Each of the eight _initialize_*_tracer calls should be wrapped in its own try/except, so one missing optional dependency only disables that one integration rather than all of them. This is a narrow fix — no config or env var changes needed, purely a startup-sequencing correction — and confirmed working when applied locally (each tracer now initializes independently; a missing Phoenix dependency no longer affects Langfuse, native tracing, or any other configured tracer).

Who can help?

No response — filed from direct debugging, not familiar with current code ownership for tracing services.