environment: move "trust_ctime" into `struct repo_config_values`

environment: move "trust_ctime" into `struct repo_config_values`

The `core.trustctime` configuration is currently stored in the global
variable `trust_ctime`, which makes it shared across repository
instances in a single process.

Store it instead in `repo_config_values`, where eagerly‑parsed
repository configuration lives. `core.trustctime` is parsed eagerly
because it is used in low‑level stat‑matching functions
(`match_stat_data()`), where a lazy parse could cause unexpected
fatal errors and complicate libification efforts. This preserves
that behavior while tying the value to the repository from which it
was read, avoiding cross‑repository state leakage and continuing the
effort to reduce reliance on global configuration state.

Update all references to use repo_config_values().

Mentored-by: Christian Couder <christian.couder@gmail.com>
Mentored-by: Usman Akinyemi <usmanakinyemi202@gmail.com>
Signed-off-by: Olamide Caleb Bello <belkid98@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>