feat(sbp2): expose the current session and command ABI to the app

[gly11]

Summary

• expose the current SBP-2 address-space and session selectors (46-49 and 52-60) through the Swift connector
• encode/decode the native-endian 20-byte command request and 16-byte result ABI
• size destructive command-result reads from the requested transfer length (up to 16 MiB) plus sense data
• show discovered SBP-2 unit metadata in the device detail UI
• add wire-format and Epson scanner metadata regression tests

Why this replaces the older fork PRs

This consolidates the still-useful parts of gly11#7 and gly11#9.

The old connector used selectors 53-61, but current main uses 52-60 and reserves selector 61 for the developer bus-reset request. It also used a fixed 512-byte command-result buffer. Current main consumes a result on read, so retrying after kIOReturnNoSpace would lose a large READ result. This version validates the request first and allocates the full result capacity before the destructive read.

Validation

Committed PR branch

• 9 focused Swift tests pass (selector ABI, request/result wire codec, 16 MiB bound, malformed result handling, Epson GT-X970 metadata)
• complete ASFWTests suite passes
• unsigned Debug macOS build passes
• no new warnings originate from the added files
• GitHub Build and Test check: passed

Live read-only MCP follow-up

With the #84 driver installed and the MCP server running, local follow-up MCP changes were exercised against the Epson V750 Pro / GT-X970 unit:

• MCP health reported ready
• asfw_sbp2_list_units discovered GUID 0x00004800004D438D
• asfw_sbp2_inspect_unit decoded ROM offset 0xF and LUN 0
• the focused MCP test slice passed 20/20

These MCP follow-up changes are still local and are not included in this PR's current head. They should be submitted separately rather than silently expanding this PR.

Remaining hardware coverage

• app-owned SBP-2 session and command execution through the new ABI has not yet been validated
• asfw_sbp2_get_session_status correctly reports capabilityUnavailable from a different MCP/user-client owner because live session state is owner-scoped
• ModernCoolScan end-to-end validation remains pending

This PR therefore remains a draft.

CI organization

Shared CI workflow cleanup is tracked separately in #88. After #88 merges, this branch should be rebased onto main so the duplicated CI commits can be dropped cleanly.