release(langgraph): prep for v1 alpha (#6025)

* Bump version of langgraph to v1.0.0a1
* Bump version of prebuilt to v0.7.0a1
* Fix tests w/ new langchain-core alpha version
* Bump min supported python version

Deprecating prebuilts tools w/ helpful IDE hinting + deprecation
messages.

---------

Co-authored-by: ccurme <chester.curme@gmail.com>

.github/workflows/_test.yml

@@ -17,7 +17,6 @@ jobs:
     strategy:
       matrix:
         python-version:
-          - "3.9"
           - "3.10"
           - "3.11"
           - "3.12"

.github/workflows/_test_langgraph.yml

@@ -12,7 +12,6 @@ jobs:
     strategy:
       matrix:
         python-version:
-          - "3.9"
           - "3.10"
           - "3.11"
           - "3.12"

.github/workflows/uv_lock_ugprade.yml

@@ -22,7 +22,7 @@ jobs:
         uses: astral-sh/setup-uv@v6
         with:
           # use minimum supported Python version
-          python-version: "3.9"
+          python-version: "3.10"
           enable-cache: true
           cache-suffix: "uv-lock-upgrade"