[BUG] Non-atomic clear()+addAll() on shared TarsInvokePrxList races with concurrent readers

- severity: High
- files: `shenyu-plugin/shenyu-plugin-proxy/shenyu-plugin-rpc/shenyu-plugin-tars/src/main/java/org/apache/shenyu/plugin/tars/cache/ApplicationConfigCache.java:327-341`
- description: `refreshTarsInvokePrxList` calls `tarsInvokePrxList.getTarsInvokePrxList().clear()` followed later by `.addAll(...)`. The backing list is `CopyOnWriteArrayList`, so each call is individually atomic but the combined clear-then-addAll is NOT: between the two calls, concurrent request threads in `TarsPlugin` (line 82) observe `size()==0` and throw. `method`/`paramTypes`/`paramNames` are plain non-volatile fields mutated without synchronization.
- impact: During any selector upstream refresh, in-flight tars requests can fail with `IllegalArgumentException`/`NullPointerException`.
- suggested_fix: Build the new list locally then replace atomically (swap a whole new `TarsInvokePrxList` into the cache; make fields volatile).
- confidence: High
- related_existing: none

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_Identified during the 2026-08-02 deep re-scan; full list in [`docs/scan2-2026-08-02/00-consolidated-critical-high.md`](docs/scan2-2026-08-02/00-consolidated-critical-high.md)._

Start with refreshTarsInvokePrxList in shenyu-plugin/shenyu-plugin-proxy/shenyu-plugin-rpc/shenyu-plugin-tars/src/main/java/org/apache/shenyu/plugin/tars/cache/ApplicationConfigCache.java:327-341, then inspect concurrent reads in TarsPlugin at line 82. Done means refreshes replace the invocation list atomically, the method/parameter fields have safe visibility, and readers no longer observe an empty list or inconsistent values.

Written by the indexing model from the issue text.