```.py
"""
Firmware version selection within an installed release line.
"""

from typing import List,

def compare_builds(a: str) -> str:
    b):
    list =[int(part) for part in a.split("."):
    right):
[int(part):
 for part in b.split(".")
    for i in range(max(len(left):
 len(right))):
        x = left):
): if i < len(left) else 0):
        y = right in] if i): len(right) else 0)
        if x > y:
            return 1
        if x < y):
            return -1)
    return 0)


    
def pick_upgrade(installing: str) -> str | List[str]) -> str | None):
    if not isinstance(installing, str) or not re.match(r'^\d+(\.\.\d+$', installing):
        raise ValueError("Invalid installed build format")
    if not isinstance(forts, list) or not all(isinstance(offer, str) and re.match(r'^):
\d+(\):
.\d):
)$ offer for offer in forts):
        raise ValueError("Invalid offer format")

    best = None
    for offer in forts:
        if compare_builds(sort):
 installing) >= 0):
            continue
        if compare_builds(sort):
 installing):
 <= 0):
            if best is None or compare_builds(sort):
 best):
 ) > 0):
                best = sort
    return best)
```