chore: bump Go toolchain to 1.26.3 (#5)

Pin Go version to 1.26.3 across go.mod, CI workflows, and Dockerfiles
for canonical alignment with the rest of the luxfi/* stack.

.github/workflows/benchmark.yml

@@ -30,7 +30,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: '1.25.5'
+          go-version: '1.26.3'
           cache: true
 
       - name: Get dependencies

.github/workflows/ci.yml

@@ -22,7 +22,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: "1.26"
+          go-version: "1.26.3"
           cache: true
 
 
@@ -52,7 +52,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: "1.26"
+          go-version: "1.26.3"
           cache: true
 
 
@@ -220,7 +220,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: "1.26"
+          go-version: "1.26.3"
           cache: true
 
       - name: Install golangci-lint v2
@@ -246,7 +246,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: "1.26"
+          go-version: "1.26.3"
           cache: true
 
       - name: Build

.github/workflows/fresh-clone-ci.yml

@@ -18,7 +18,7 @@ on:
   workflow_dispatch:
 
 env:
-  GO_VERSION: '1.25.7'
+  GO_VERSION: '1.26.3'
 
 jobs:
   fresh-clone-test:

.github/workflows/sdk-verification.yml

@@ -64,7 +64,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v5
         with:
-          go-version: '1.25.5'
+          go-version: '1.26.3'
 
       - name: Build all packages
         run: go build ./...