Code formatting and style cleanup in 6502.{h,cc}

[wfd3]

Description

Several minor code formatting and style issues that should be cleaned up for consistency.

Issues

1. Mixed indentation in struct definition

Location: 6502/6502.h:344-350

struct instruction {
    const char *name;
    AddressingMode addrmode;  // Inconsistent indentation
    Byte bytes;

The struct has mixed tabs/spaces.

2. Unnecessary blank line

Location: 6502/6502.cc:254-256

bool MOS6502::validInstruction(const Byte opcode) {
    return _instructions.count(opcode) != 0;
           // Extra whitespace here
}

3. Inconsistent parameter const usage

Some pass-by-value parameters are marked const, others aren't. Should be consistent throughout.

4. Magic numbers in pushPS()

Location: 6502/6502.cc:314-315

constexpr Byte BreakBit  = 1 << 4;
constexpr Byte UnusedBit = 1 << 5;

These could be class-level constants since they're part of the 6502 specification.

Priority

Low - these are cosmetic issues that don't affect functionality.