Refactor Bun installation checks in Jenkinsfile

- Renamed the function from `ensureBunInstalled` to `checkBun` for clarity.
- Simplified the Bun version check process by removing installation commands, focusing solely on verifying Bun's presence.
- Updated stage names in the CI pipeline to reflect the new function and improve readability.

Jenkinsfile

@@ -16,23 +16,11 @@ def withBun(Closure body) {
     }
 }
 
-def ensureBunInstalled() {
+def checkBun() {
     if (isUnix()) {
-        sh '''
-            set -eu
-            export BUN_INSTALL="${HOME}/.bun"
-            export PATH="${BUN_INSTALL}/bin:${PATH}"
-            if ! command -v bun >/dev/null 2>&1; then
-                curl -fsSL https://bun.sh/install | bash
-            fi
-            bun -v
-        '''
+        sh 'bun -v'
     } else {
-        bat '''
-            where bun >nul 2>nul || %SystemRoot%/System32/WindowsPowerShell/v1.0/powershell.exe -NoProfile -ExecutionPolicy Bypass -Command "irm bun.sh/install.ps1 | iex"
-            set PATH=%USERPROFILE%/.bun/bin;%PATH%
-            bun -v
-        '''
+        bat 'bun -v'
     }
 }
 
@@ -56,8 +44,8 @@ def buildLinux() {
             }
 
             withBun {
-                stage('Setup Bun (Ubuntu)') {
-                    ensureBunInstalled()
+                stage('Check Bun (Ubuntu)') {
+                    checkBun()
                 }
 
                 stage('Install Dependencies (Ubuntu)') {
@@ -90,8 +78,8 @@ def buildOnLabel(label, buildCommand) {
             }
 
             withBun {
-                stage("Setup Bun (${label})") {
-                    ensureBunInstalled()
+                stage("Check Bun (${label})") {
+                    checkBun()
                 }
 
                 stage("Install Dependencies (${label})") {
@@ -127,7 +115,7 @@ def setBuildNameFromPackageVersion() {
         stage('Set Build Name') {
             checkout scm
             withBun {
-                ensureBunInstalled()
+                checkBun()
                 def version = sh(
                     script: "bun --eval \"console.log(JSON.parse(await Bun.file('package.json').text()).version)\"",
                     returnStdout: true