Move Ready in time before handler initialization (#88235)
## Move "Ready in X" log before config loading and eliminate duplicate
`loadConfig` calls
### What?
Reorder the dev server startup flow so the "Ready in X" log appears
before loading the user's `next.config.js`, and eliminate duplicate
`loadConfig` calls in both dev and build paths.
### Why?
Previously, the "Ready in X" time included the time spent loading and
evaluating the user's `next.config.js` file. This made the framework
appear slower than it actually is, especially for projects with complex
config files or slow config evaluation.
Additionally, config was being loaded twice:
- **Dev server**: Once in `getStartServerInfo()` just for logging, then
again in `getRequestHandlers()`
- **Build**: Once for the main build, then again in
`getStartServerInfo()` just for logging
### How?
**Before:**
```
1. getStartServerInfo() → loadConfig #1 (slow - blocks on next.config.js)
2. logStartInfo() → logs version, URLs, experimental features
3. "Ready in X" ← time includes config loading
4. getRequestHandlers() → loadConfig #2
```
**After:**
```
1. logStartInfo() → logs version, URLs, envInfo (no config needed)
2. "Ready in X" ← reflects actual framework startup time
3. getRequestHandlers() → loadConfig (once)
4. logExperimentalInfo() → logs experimental features
```
**Changes:**
- Split `logStartInfo` into two functions:
- `logStartInfo()` - basic info (version, URLs, env) - no config needed
- `logExperimentalInfo()` - experimental features and cacheComponents
- Removed `getStartServerInfo()` which was loading config unnecessarily
- Added `experimentalFeatures` and `cacheComponents` to
`ServerInitResult` so they can be passed back after config loads
- In build, added `reportExperimentalFeatures` callback to the existing
`loadConfig` call instead of loading config twice
---------
Co-authored-by: Vercel <vercel[bot]@users.noreply.github.com>
