Restructure Memory API with sub-objects for trajectory (and future memory types)

[gemenerik]

Currently cf.memory().write_trajectory(...) and cf.memory().write_compressed_trajectory(...) live directly on Memory. A cleaner API would nest them:

Current

await cf.memory().write_trajectory(segments)
await cf.memory().write_compressed_trajectory(start, segments)

Proposed

await cf.memory().trajectory().write(segments)
await cf.memory().trajectory().write_compressed(start, segments)