drv: deprecate tdma_client and tdma_server

[geonnave]

Marks the TDMA client and server radio drivers as deprecated and points
readers at the bare-radio + Mari-compatible frame layout that replaced
them in DotBots/DotBot-firmware#410. TDMA was a swarm-coordination
placeholder; the Mari TSCH link layer now owns that role end-to-end,
and bare DotBot apps that previously sat on top of drv/tdma_client
have all been migrated to talk to drv/radio directly with the
21-byte header from drv/frame.h (added in #21). The nRF5340 net-core
IPC multiplexer in DotBot-firmware also dropped its TDMA dispatch in
the same PR (#410), so once it merges, the only remaining references
to drv/tdma_* in the workspace are the example projects shipped
alongside the drivers in this repo (projects/01drv_tdma_{client,server}/).

This PR is documentation-only — no functional change. **Deprecated.**
prose paragraph at the top of each header's @defgroup block describing
what to use instead. (Initially used @deprecated Doxygen tags but those
generate cross-references to a "Deprecated List" page that doesn't exist
in this Sphinx setup, causing Breathe to error on undefined labels.)

The follow-up cleanup PR is dotbot-libs-internal:

1. Drop the DB_IPC_TDMA_* enum values + ipc_tdma_{client,server}_data_t
   struct fields from bsp/ipc.h (nothing dispatches them anymore after
   #410).
2. Delete drv/tdma_client/, drv/tdma_server/, the 01drv_tdma_*
   example projects, and matching Makefile entries.

Validated locally: make BUILD_TARGET=nrf52840dk BUILD_CONFIG=Debug
green; clang-format clean.