enable-resume (#3537)

Adding the ability to resume conversations.
we have one verb `resume`. 

Behavior:

`tui`:
`codex resume`: opens session picker
`codex resume --last`: continue last message
`codex resume <session id>`: continue conversation with `session id`

`exec`:
`codex resume --last`: continue last conversation
`codex resume <session id>`: continue conversation with `session id`

Implementation:
- I added a function to find the path in `~/.codex/sessions/` with a
`UUID`. This is helpful in resuming with session id.
- Added the above mentioned flags
- Added lots of testing

codex-rs/exec/Cargo.toml

@@ -46,4 +46,6 @@ core_test_support = { path = "../core/tests/common" }
 libc = "0.2"
 predicates = "3"
 tempfile = "3.13.0"
+uuid = "1"
+walkdir = "2"
 wiremock = "0.6"