Load per-version wire packages lazily from the methods surface maps

mcp_types.methods imported both generated wire packages (_v2025_11_25 and
_v2026_07_28, roughly 200 pydantic models each) at module import solely to
fill the surface maps' values, although a connection negotiates exactly one
protocol version and nothing reads a value at import time.

The map rows now record the wire type's attribute name; the package a row
lives in follows from the key's protocol version and is imported by a cached
lookup on the first row read, then cached per row. The public maps stay
MappingProxyType objects over the resolved rows (same protocol, repr and
equality as before), so importing mcp_types.methods - and therefore mcp,
mcp.types and every entry point above them - no longer builds any wire
package; the first message parsed for a version builds that version once.

The elicitation module's single wire-schema import moves into the function
that uses it for the same reason.

Author: maxisbey