refactor(tazjin/tgsa): factor out cache access helper r/4075

factor out a function to access telegram posts from the cache,
fetching them anew if required.

a small behavioural change means that the program now takes a write
lock when fetching a post, to avoid simultaneously fetching the same
post many times (quite likely once it serves image redirects).

Change-Id: If9c1429f86fb118dab90834f349cb222709c3a31
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5608
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

0 files changed, 0 insertions, 0 deletions