Read file content for the requested line range.
Implementations must tolerate degenerate windows rather than raising:
a negative offset reads from the first line, and a non-positive
limit returns empty content with every pagination field unset.
deepagents.backends.utils.normalize_read_bounds clamps both bounds for
implementations that slice in Python.
Implementations must also set start_line whenever they return
line-numberable text. The middleware falls back to deriving the gutter
from offset when start_line is unset, which only yields a valid
1-indexed gutter for windows the backend actually sliced.
Absolute path to the file to read. Must start with '/'.
Line number to start reading from (0-indexed).
Maximum number of lines to read.
