core/crypto: Stop using context.temp_allocator

The max digest size for the foreseeable future will be 512 bits, and the
max block size is currently 1152 bits (SHA3-224).  If people add more
exotic hash algorithms without bumping the constants when required,
tests will fail.

The stream buffer will currently be 576 bytes, which is "fine" to just
stick on the stack, and is a sensible multiple of the more common block
size of 64 bytes.

tests/core/crypto/test_core_crypto_hash.odin

@@ -514,6 +514,31 @@ test_hash :: proc(t: ^testing.T) {
 
 		algo_name := hash.ALGORITHM_NAMES[algo]
 
+		// Ensure that the MAX_(DIGEST_SIZE, BLOCK_SIZE) constants are
+		// still correct.
+		digest_sz := hash.DIGEST_SIZES[algo]
+		block_sz := hash.BLOCK_SIZES[algo]
+		expect(
+			t,
+			digest_sz <= hash.MAX_DIGEST_SIZE,
+			fmt.tprintf(
+				"%s: Digest size %d exceeds max %d",
+				algo_name,
+				digest_sz,
+				hash.MAX_DIGEST_SIZE,
+			),
+		)
+		expect(
+			t,
+			block_sz <= hash.MAX_BLOCK_SIZE,
+			fmt.tprintf(
+				"%s: Block size %d exceeds max %d",
+				algo_name,
+				block_sz,
+				hash.MAX_BLOCK_SIZE,
+			),
+		)
+
 		// Exercise most of the happy-path for the high level interface.
 		rd: bytes.Reader
 		bytes.reader_init(&rd, transmute([]byte)(data_1_000_000_a))