fix(openai,groq,openrouter): use is-not-None checks in usage metadata token extraction (#36500)

Python's `or` operator treats `0` as falsy, so
`token_usage.get("total_tokens") or fallback` silently replaces a
provider-reported `total_tokens=0` with the computed sum of input +
output tokens. Providers can legitimately report zero tokens (e.g.,
cached responses, empty completions).

The same pattern exists in the dual-key lookups for
`input_tokens`/`output_tokens` in Groq and OpenRouter. While current
APIs don't return both key formats simultaneously (making the `or`-chain
functionally correct today), the semantics are still wrong; `0` should
not fall through to a fallback.

## Changes

- Replace `x.get(key) or fallback` with explicit `is not None` checks in
`_create_usage_metadata` across `langchain-openai`, `langchain-groq`,
and `langchain-openrouter` for `input_tokens`, `output_tokens`, and
`total_tokens`
- Fix a concrete bug in the `total_tokens` path: a provider-reported `0`
was silently replaced by the computed sum
- Harden dual-key lookups in Groq and OpenRouter to correctly preserve
zero values from the preferred key, should both key formats ever coexist
- Update OpenAI's single-key extraction for consistency — the old `or 0`
pattern happened to produce correct results (`0 or 0 == 0`) but was
semantically wrong

libs/partners/openai/uv.lock

@@ -550,7 +550,7 @@ wheels = [
 
 [[package]]
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-version = "1.2.13"
+version = "1.2.15"
 source = { editable = "../../langchain_v1" }
 dependencies = [
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@@ -578,7 +578,7 @@ requires-dist = [
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     { name = "langchain-together", marker = "extra == 'together'" },
     { name = "langchain-xai", marker = "extra == 'xai'" },
-    { name = "langgraph", specifier = ">=1.1.1,<1.2.0" },
+    { name = "langgraph", specifier = ">=1.1.5,<1.2.0" },
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@@ -614,7 +614,7 @@ typing = [
 
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+version = "1.2.25"
 source = { editable = "../../core" }
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@@ -806,7 +806,7 @@ typing = [
 
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+version = "1.1.5"
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@@ -836,15 +836,15 @@ wheels = [
 
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+version = "1.0.9"
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