The role of the series resistors for ESD protection
The role of R1 and R2 resistors is to limit ESD currents for extra level of ESD protection.

The R1 limits the spike current into TVS diode. When you apply a 15-kV ESD event, the current spike across the TVS will be 15,000/100 = 150 A. A typical TVS diode (like Littlefuse SP4020, 3.3V breakdown) has the dynamic resistance of about 0.4 Ohms, so the spike will result in about 60 V peak amplitude. This might be damaging to GPIO internals of the connected IC.

All ICs do have internal ring of ESD protection, typically using "clamping diodes", and they do have obvious electrical limits. The second resistor R2 will limit the ESD current spike to 60/100 = 600 mA, and this short pulse is less likely to destroy the GPIO of the IC.

The values of resistors obviously depend on signal bandwidth on that particular GPIO. Pin/package capacitances will degrade the signal, and the values usually are a trade-off between acceptable signal integrity and required level of ESD protection. You might need no resistors at all if your product has properly-designed shielding.