fix(doctor): count RAM channels from Locator so EPYC isn't mis-flagged single-channel

[VijitSingh97]

Problem

On a fully-populated 8-channel EPYC 7642 (8 DIMMs, one per channel — the optimal layout), doctor printed a false warning:

! RAM is single-channel (8 module(s), 1 channel) — RandomX wants ≥2 channels...

The board is genuinely 8-channel: it sustains ~36,880 H/s on RandomX (single-channel would be far lower), and exposes one Locator per channel.

Root cause

_mem_summary() counted memory channels as the number of distinct Bank Locator values from dmidecode -t memory. Desktop boards encode the channel there (BANK 0/P0 CHANNEL A), so the heuristic works. But server boards (EPYC/Threadripper) repeat one Bank Locator: BANK 0 for every DIMM and instead carry the channel in the Locator field's letter group:

Locator: DIMM_P0_A0   ... DIMM_P0_H0   (channels A..H)
Bank Locator: BANK 0  (same for all 8)

So the count collapsed to 1.

Fix

_mem_summary now counts distinct channels in both fields and reports whichever is larger:

• New /^[ \t]*Locator:/ awk rule (anchored so it doesn't also match Bank Locator:) extracts the channel designator via match(v,/[A-Za-z][0-9]+$/) — the letter immediately before the trailing slot number (DIMM_P0_A0→A, DIMM A1→A), upper-cased into a separate set.
• At END, channels = max(bank-locator channels, locator channels).

Taking the max keeps existing desktop dual-channel detection intact (Bank Locator path untouched) and can only raise the count toward truth — a genuine single-channel layout still reads as 1, since its populated DIMMs share one channel letter.

Tests (dependency-free, in tests/run.sh)

• EPYC fixture — 8 × DIMM_P0_[A-H]0, all Bank Locator: BANK 0 → asserts 8 modules across 8 channels and no single-channel warning.
• Desktop-Locator fixture — channel carried only in the Locator (DIMM A1/DIMM B1, shared BANK 0) → asserts 2 channels / no warning, proving the Locator path works independently of Bank Locator.
• Existing single-channel and dual-channel Bank Locator tests unchanged and still pass.

Verification

• make lint (shellcheck + shfmt -i 4): clean
• make test-suite: 602 passed, 0 failed

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