v1.1.0 - Offline input, compatibility warnings, physical ID, OC guidance

The usefulness half of the same v1.0.0 review: v1.0.1 fixed correctness
and safety, this addresses "what's actually missing for the stated use
case" (a mixed kit that barely boots, being diagnosed one module at a
time). Every new byte offset used here (moduleType, busWidth/ECC bit,
serial number) was independently cross-checked against the live reference
kit's decode-dimms output before being trusted -- same discipline as
every previous release.

New features

• Offline SPD file input. spd_matchtable.py stick1.bin stick2.bin ...
  decodes dumps instead of live sysfs -- the actual gap for a system that
  only boots with some sticks installed, or for combining dumps taken one
  module at a time, from another machine, or shared in a forum post.
  Produce one with cat /sys/bus/i2c/drivers/ee1004/1-0050/eeprom > stick.bin.
• Module-type and ECC mismatch warnings. Mixing RDIMM/LRDIMM with
  UDIMM, or ECC with non-ECC, are the #1 and #2 reasons a mixed kit fails
  to POST at all rather than just underperforming -- previously silent,
  now a loud !! warning right after the modules table.
• Physical identification columns: capacity (computed from density,
  width, and rank -- verified against this project's own 3 known reference
  capacities before trusting the formula), serial number, and
  manufacture date, so "1-0053 is your problem stick" can actually be
  matched to a physical DIMM without guessing.
• OC-boundary markers. A new section lists, per candidate MT/s, which
  installed modules are being pushed beyond their own declared JEDEC base
  spec -- previously the match table alone gave no indication that half
  the "candidates" were an overclock for some fraction of the kit.
• "Suggested starting point": a ready BIOS line at the SPD-guaranteed
  ceiling, plus a clearly separate second line for generic secondary
  timings SPD doesn't encode (tCWL = CL-1, a ~7.5ns tRTP estimate,
  tCCD_S=4, and a rank/DIMM-count-based command-rate guess) -- labeled
  as inference, not measurement.
• --json now includes the same computed worstCaseNs, matchTableCycles,
  and compatibilityWarnings the text report shows, not just the raw
  per-module decode -- so scripts can consume the tool's actual product.

Fixes and polish from the same review

• Frequency-labeling rounding artifact removed. 2000/tCKmin on a
  JEDEC-rounded tCKmin (e.g. DDR4-2400's published 0.833ns) doesn't
  invert cleanly and previously showed as "2401 MT/s" everywhere,
  including feeding real cycle math in the new cheat-sheet line. Snapped
  to the nearest standard JEDEC speed bin within a tight tolerance instead
  -- ceiling, match-table columns, and cheat sheet now agree exactly.
• Natural slot/filename sorting (2-0050 before 10-0050, not the
  reverse) instead of plain lexical sort.
• Soft sanity warnings for a --freqs value outside a realistic DDR4
  range, or below any installed module's minimum supported speed
  (tCKmax exceeded) -- previously silent.
• --selftest grew from 39 to 49 checks: natural sort ordering, the
  capacity formula, module-type/ECC decoding, the frequency-snapping fix,
  both compatibility-mismatch detectors (plus a no-false-positive check on
  a matched kit), and a round-trip check that offline file input decodes
  identically to live sysfs reads.