Support for Lilygo T3S3 LR1121

[BetaFloof]

I accidentally bought a Lilygo T3S3 with an LR1121 instead of the already supported SX1262, so I tried implementing it myself since radiolib supports it.

I basically copied the configuration for the T3S3 SX1262 and adjusted it to work with the LR1121. It's mostly code adapted from existing variants using the LR1110.

Using a second node (RPi Pico + SX1262, fw version 1.9.0) I verified the functionality of:

• BLE companion radio
• USB companion radio
• Terminal chat
• Room server
• Repeater (limited test)

I wasn't able to test chatting over the repeater because I currently don't have enough nodes, but serial commands, advertising, connecting as guest & admin and requesting status all worked.

[recrof]

just few notes:

1. getPacketLength in CustomLR1121 can be removed - newest radiolib fixed it
2. LR1121 includes 2 radios - 2.4Ghz and sub-ghz one. the firmware/app does not know one radio supports max 20dBm(2.4Ghz) and 22dBm(sub-ghz).. if you switch the frequency to 2.4, you will get weird behaviour because of this.