:sig
StringMap split_kv(String s, char separator = '=', bool trim_whitespace = true, bool uppercase_keys = false)

:params
s : input containing one key/value pair per line
separator : character separating each key from its value
trim_whitespace : trim keys and values when true
uppercase_keys : uppercase keys when true
return value : map of parsed keys and values

:see
>string
split
split_http_headers

:content
Parses simple line-based key/value text into a `StringMap`.

Each non-empty line is split on the first `separator`. Lines without the separator are kept with an empty value.

Example:

```uce
StringMap cfg = split_kv("host = localhost\nport = 8080");
// cfg["host"] == "localhost"
// cfg["port"] == "8080"
```

This is useful for small config files, metadata blocks, and tests that need predictable key/value parsing.