Add typed array literals and numeric hex literals

[someone235]

Closes #159

Introduce explicit types for array literals and redefine hexadecimal literals as numerals. Byte sequences now require explicit casts, while pubkey, sig, and datasig accept correctly
sized hex literals directly.

Language Behavior Changes

• Array literals now use T{...} instead of untyped [...] syntax.

int[] dynamic = int[]{1, 2, 3};
int[3] inferred = int[_]{1, 2, 3};
int[3] fixed = int[3]{1, 2, 3};

T[]{...} produces a dynamic array, T[_]{...} infers a fixed size, and T[N]{...} requires exactly N elements.

• Nested array literals retain their element dimensions.

byte[2][_] values = byte[2][_]{byte[2](0x0102), byte[2](0x0304)};

Nested elements must have compatible types and equal fixed dimensions.

• Hex literals up to eight bytes are now numeric literals.

int mask = 0xff00;
byte tag = 0xff;

They no longer implicitly produce byte arrays. Raw bytes require an immediate byte-array cast:

byte[] data = byte[](0x01020304);
byte[_] fixedData = byte[_](0x010203040506070809);

Hex literals longer than eight bytes remain invalid unless immediately cast to a byte array or fixed byte-sequence type.

• Fixed byte-sequence types accept direct hex casts with exact size validation.

pubkey key = pubkey(0x0202020202020202020202020202020202020202020202020202020202020202);
sig signature = sig(0x...);         // exactly 65 bytes
datasig dataSignature = datasig(0x...); // exactly 64 bytes

• Casts between fixed arrays with known, unequal sizes are rejected consistently for every element type.