Header Parsing: Parse HTTP-Style Headers from a Raw Request String

Question

## Problem

Given a raw HTTP request string, parse it into: `method`, `path`, `http_version`, and a `headers` dict. Header names are case-insensitive; normalize them to lowercase. Stop at the blank line separating headers from body.

```python
def parse_request(raw: str) -> dict:
    # return {"method": str, "path": str, "version": str, "headers": dict}
    pass
```

**Example:**
```
raw = (
  "GET /api/users HTTP/1.1
"
  "Host: example.com
"
  "Content-Type: application/json
"
  "Authorization: Bearer token123
"
  "
"
  "{"key": "value"}"
)

Output:
{
  "method":  "GET",
  "path":    "/api/users",
  "version": "HTTP/1.1",
  "headers": {
    "host":           "example.com",
    "content-type":   "application/json",
    "authorization":  "Bearer token123"
  }
}
```

## Follow-ups

1. How do you handle multi-value headers (e.g. multiple `Set-Cookie` lines) — list or last-wins?
2. What happens when a header line has no `:` separator — should you skip it or raise an error?
3. How would you extend this to also parse and return the request body?
4. How do you guard against maliciously large headers (header injection / DoS)?

Header Parsing: Parse HTTP-Style Headers from a Raw Request String

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