refactor: eliminate comptime DB generics; add phantom access fix

Replace Journal(DB)/Context(DB)/EvmFor(DB) comptime generics with a
concrete Database vtable (ptr + fn pointers). Journal, Context, and Evm
are now single concrete types — no more per-DB monomorphization.

The @hasDecl pattern for optional DB methods is eliminated entirely. The
one remaining optional capability (hasNonZeroStorageForAddress for CREATE
collision detection) lives in the Database vtable as a nullable fn ptr.

Also fixes phantom BAL entries at the opcode level: CALL now uses a
worst-case getCallGasCost pre-check (assumes account non-existent) before
loading the target, EXTCODECOPY moves all gas charges before codeInfo(),
SELFDESTRUCT adds a worst-case pre-check before h.selfdestruct(), and
CREATE moves the Amsterdam balance check before js.loadAccount(new_addr).
untrackAddress/forceTrackAddress and bal_untracked are fully removed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: Gabriel-Trintinalia

examples/simple_contract.zig

@@ -18,7 +18,7 @@ pub fn main() !void {
     defer db.deinit();
 
     // Create a context with Prague specification
-    var ctx = context.DefaultContext.new(db, primitives.SpecId.prague);
+    var ctx = context.DefaultContext.new(database.Database.forDb(database.InMemoryDB, &db), primitives.SpecId.prague);
 
     // Create a simple contract that adds two numbers
     // PUSH1 0x05  (push 5 onto stack)