truncate_string returns a string longer than max_length for small limits

Describe the bug

nat.utils.string_utils.truncate_string(text, max_length) is documented to
"truncate a string to a maximum length," but for max_length < 3 it returns a
string longer than max_length. When the input needs truncating it does:

return text[:max_length - 3] + "..."

For max_length < 3, max_length - 3 is negative, so text[:max_length - 3]
slices from the end of the string instead of the start, and the "..." is then
appended — producing output that is both longer than max_length and cut from
the wrong end.

Reproduction

from nat.utils.string_utils import truncate_string

truncate_string("abcdefghij", 2)   # -> 'abcdefghi...'  (12 chars for max_length=2)
truncate_string("abcdefghij", 1)   # -> 'abcdefgh...'   (11 chars for max_length=1)

Expected: the result never exceeds max_length (e.g. "..", "." — as much of
the ellipsis as fits).

For max_length >= 3 the function already behaves correctly
(truncate_string("abcdefghij", 5) == "ab..."); only small limits are affected.

Proposed fix

Guard the small-max_length case so the ellipsis is truncated to fit instead of
using a negative slice, keeping the existing behavior for max_length >= 3.
Happy to send a small PR with tests.

Start at nat.utils.string_utils.truncate_string and reproduce the small-limit cases described in the issue. Add focused tests for max_length values 1 and 2, while confirming the existing max_length >= 3 behavior remains unchanged; done means the result never exceeds max_length and the tests pass.