fix: language version IDs, cache crash, and stress session restore (#352)

## Problem

Codeforces language version IDs were wrong (pointed at old compiler
versions), `LANGUAGE_VERSIONS` was incomplete for most platforms, the
contest picker crashed when `supports_countdown` was stored as a
non-table entry, and `:CP stress` restored a broken IO view on exit.

## Solution

Correct CF `programTypeId` values and default to C++20. Add
`LANGUAGE_VERSIONS` entries for all six platforms. Guard
`get_contest_summaries` against non-table cache entries. Call
`ensure_io_view()` after stress session restore. Shorten the stress
terminal buffer name to a readable `term://stress.py` format.

1621.rs

@@ -0,0 +1,10 @@
+  use std::io::{self,Read};
+  fn main(){
+  let mut s=String::new();
+  io::stdin().read_to_string(&mut s).unwrap();
+  let s=s.trim().as_bytes();
+  let(mut mx,mut c)=(1usize,1usize);
+  for i in 1..s.len(){if s[i]==s[i-1]{c+=1;}else{c=1;}if c>mx{mx=c;}}
+  println!("{}",mx);
+  }
+