fix: bounds check in Delete to prevent index out of range panic

[Yanhu007]

Fixes #274

Problem

Delete accesses data[endOffset+tokEnd] without checking if the index is within bounds. tokenEnd() returns len(data) when no terminator is found, so endOffset+tokEnd can exceed the slice length, causing a panic:

panic: runtime error: index out of range [9] with length 9

Found by fuzzing.

Fix

Add a bounds check before accessing data[endOffset+tokEnd]:

if endOffset+tokEnd >= len(data) {
    return data
}

All existing tests pass.