feat: make bufflength optional on write and search methods

[JeanExtreme002]

Summary

bufflength is now optional (defaults to None) on write_process_memory, search_by_value, search_by_value_between and search_by_addresses. Previously it was a required positional parameter sitting before the value, forcing calls like write_process_memory(addr, str, None, "hi"). Now you can simply write:

process.write_process_memory(addr, str, value="hi")
process.search_by_value(int, value=100)
process.search_by_value_between(int, start=10, end=20)
process.search_by_addresses(int, addresses=[0x1000, 0x1004])

Behavior

• Numeric types (int/float/bool) fall back to their default width (4/8/1) when bufflength is omitted.
• str/bytes on search_by_value / search_by_value_between infer the width from the value being searched (UTF-8 for str; the longer endpoint for a range search).
• search_by_addresses still requires an explicit size for str/bytes — there is no value to infer the width from, only addresses to read (same as read_process_memory).
• A new UNSET sentinel keeps value / start / end / addresses required while bufflength carries a default; omitting them raises a clear TypeError.
• Positional calls keep working unchanged — write_process_memory(addr, int, 4, 99) and search_by_value(int, 4, 100) are fully backward compatible.

Changes

• util/convert.py: UNSET sentinel and resolve_bufflength_for_value helper; prepare_write validates a missing value.
• process/abstract.py + win32/linux/macos backends: optional bufflength, sentinel-defaulted required args, updated docstrings.
• Docs (read-write, searching, openprocess, index) updated; no more positional-None examples.
• Tests added covering keyword calls, str/bytes inference, positional backward compatibility, and the missing-argument errors.

Verification

• make type-check (mypy): clean.
• Relevant test suite: 93 passed, 4 skipped (platform-specific).