Find safe travel intervals between planet influences

You are planning a space route along a one-dimensional line (the x-axis). You are given a list of planets. Each planet is represented by an integer pair \((c, r)\): - `c` is the coordinate of the planet's center on the x-axis. - `r` is a non-negative integer radius of its gravitational influence. A point `x` on the x-axis is **unsafe** for a space traveler if it lies within the gravitational influence of at least one planet: \[ |x - c_i| \le r_i \quad \text{for some planet } i \] Equivalently, each planet makes the interval \([c_i - r_i,\; c_i + r_i]\) unsafe. Task: - Consider the entire real line as the possible travel path. - Compute all **maximal continuous intervals** on this line where the traveler is **safe**, i.e., points not covered by any planet's unsafe interval. - Return these safe intervals as a sorted list of disjoint intervals. Representation details: - Represent each safe interval as a pair `(start, end)` with `start < end`. - Intervals may be unbounded on the left or right: - Use `-∞` for an interval unbounded to the left (e.g., `(-∞, a)`). - Use `+∞` for an interval unbounded to the right (e.g., `(b, +∞)`). You may assume the input list of planets can be in any order and may contain overlapping or nested gravitational ranges. Return the safe intervals in increasing order of `start`.