ci(infra): harden Dependabot version-bound preservation (#37510)

Dependabot has been stripping upper/lower bounds from internal
`langchain-*` deps in partner `pyproject.toml` files (e.g. #37288
reduced `langchain-core>=1.3.2,<2.0.0` to bare `langchain-core`). Locks
down the config so bumps preserve existing specifiers, and restores the
bounds it already mangled across the monorepo.

## Changes
- Add `versioning-strategy: increase` to every `uv` ecosystem block in
`.github/dependabot.yml` so future bumps move the lower bound in place
instead of rewriting the constraint.
- Ignore workspace-internal packages (`langchain-core`, `langchain`,
`langchain-classic`, `langchain-text-splitters`, `langchain-tests`,
`langchain-model-profiles`) on every `uv` block — these are editable
installs from local paths and their published constraints are
hand-curated for release, not Dependabot's to bump.
- Restore stripped bounds across all `libs/` packages — runtime
`dependencies` and every dep group (`test`, `dev`, `test_integration`,
`typing`, `lint`) — to `>=1.4.0,<2.0.0` for `langchain-core` and
`>=1.0.0,<2.0.0` for the other internal packages.

libs/text-splitters/pyproject.toml

@@ -41,7 +41,7 @@ Reddit = "https://www.reddit.com/r/LangChain/"
 [dependency-groups]
 lint = [
     "ruff>=0.15.0,<0.16.0",
-    "langchain-core"
+    "langchain-core>=1.4.0,<2.0.0"
 ]
 typing = [
     "mypy>=1.19.1,<1.20.0",
@@ -52,7 +52,7 @@ typing = [
 ]
 dev = [
     "jupyter<2.0.0,>=1.0.0",
-    "langchain-core"
+    "langchain-core>=1.4.0,<2.0.0"
 ]
 test = [
     "pytest>=9.0.3,<10.0.0",
@@ -62,7 +62,7 @@ test = [
     "pytest-asyncio>=1.3.0,<2.0.0",
     "pytest-socket>=0.7.0,<1.0.0",
     "pytest-xdist<4.0.0,>=3.6.1",
-    "langchain-core",
+    "langchain-core>=1.4.0,<2.0.0",
 ]
 test_integration = [
     "spacy>=3.8.13,<4.0.0",