Prevent build deadlocks on shared circular extends chains - #64835

Concurrent projects entering a circular extends chain at different points can each hold a cache-entry lock while waiting for the other. The per-parser cycle check cannot detect this cross-goroutine deadlock.

• Cache: Parse misses without holding locks, then publish completed entries with LoadOrStore. Concurrent misses may duplicate parsing.
• Regression coverage: Synchronize two project parses entering the same cycle at different configs and require TS18000 from both.

• Fixes tsc -b can hang when two referenced projects extend into one circular extends chain #64833