fix(java): wrap bare rethrows of checked exceptions

[kroitor]

What broke

printThrowStatement's Identifier branch emits a bare rethrow (throw e) verbatim. In the transpiled ccxt Java, method bodies live inside CompletableFuture lambdas which cannot declare throws, so rethrowing the caught (checked) java.lang.Exception fails compilation:

error: unreported exception Exception; must be caught or declared to be thrown
    try { ... } catch (Exception e) { throw e; }
                                      ^

First real-world trigger: the mexc ws authenticate fix (ccxt/ccxt#29392) — the first bare rethrow ever transpiled to Java in ccxt — whose auto-committed emission broke ccxt's java.yml Build Project step (failing run).

Fix

Emit a conditional wrap in the Identifier branch:

throw (e instanceof RuntimeException ? (RuntimeException)e : new RuntimeException(e));

• unchecked exceptions — including all ccxt error types, which extend RuntimeException — rethrow with identity intact, so upstream catch dispatch on ccxt exception types is unaffected
• genuinely checked exceptions get wrapped with the original as the cause
• other language emitters untouched (their targets accept bare rethrow)

Verified against ccxt

• patched emitter → regenerated java/lib/.../pro/MexcCore.java → emits the conditional form at the previously-broken site
• isolated javac proof: the wrapped construct compiles inside a supplyAsync lambda; the previous emission reproduces the exact CI error