feat(analysis): add validated Gwyddion parity capabilities

[kegouro]

Summary

This pull request adds a validated Gwyddion-parity foundation for SPMKit,
covering leveling, background-estimation, morphology, compatibility auditing,
and frozen scientific evidence.

Implemented capabilities

• Arc Revolution Background
• Sphere Revolution Background
• Flatten Base
• Median Background
• Flat-disc Opening and Closing
• Path Level
• Align Rows statistics:
  • Median
  • Median of differences
  • Trimmed mean
  • Trimmed mean of differences
• GwyCompat source-audit foundation

Scientific methodology

Each completed parity capability follows a bounded evidence workflow:

1. literature and mathematical reconstruction;
2. inspection of the relevant Gwyddion 2.71 source;
3. external execution against installed Gwyddion;
4. independent oracle construction;
5. frozen fixtures and provenance;
6. private numerical implementation;
7. public context-preserving API;
8. focused and project-wide regression verification.

Evidence and production changes are preserved as separate atomic commits.

Align Rows numerical profiles

The production contract follows portable source semantics.

• Portable profile:

  • 64/64 corrected arrays bitwise exact
  • 3888/3888 elements bitwise exact
  • requested backgrounds 8/8 arrays and 504/504 elements bitwise exact

• Installed Gwyddion 2.71 fast-math profile:

  • 61/64 arrays bitwise exact
  • 3757/3888 elements bitwise exact
  • remaining differences are restricted to the frozen signed-zero cases and
    two independently explained GCC fast-math reassociation cases

SPMKit deliberately does not emulate compiler-specific fast-math behavior.

Verification

Final repository closure:

• 1305 tests passed
• 31 tests skipped
• Ruff passed
• Black passed
• Mypy passed
• wheel build passed
• sdist build passed
• isolated wheel installation/import passed
• public import smoke passed
• relative documentation links passed
• frozen NPZ payload hashes unchanged
• no unauthorized local paths or cache artifacts remain
• no runtime dependency on Gwyddion, SciPy, frozen fixtures, subprocess probes,
  network access, or compiler-profile emulation was introduced

Compatibility

The historical generic align_rows(channel, method="median") contract remains
backward compatible for median and mean calls.

The four explicit gwyddion_align_rows_* functions are the bounded
cross-validated Gwyddion surfaces. The generic dispatcher is not claimed to be
universally Gwyddion-compatible.

Evidence scope and non-claims

Claims are limited to their documented finite frozen campaigns.

This pull request does not claim:

• universal numerical equivalence;
• non-finite input parity unless explicitly documented;
• parity with every Gwyddion build or future version;
• GUI or publication-workflow parity;
• performance equivalence;
• binary compatibility;
• automatic translation of arbitrary Gwyddion modules.

Review guidance

The commit history should be reviewed by capability family:

1. reconnaissance and frozen evidence;
2. private numerical kernel;
3. public API;
4. documentation and scientific status;
5. integration and hygiene closure.

Please preserve the atomic commit history. A merge commit is preferred over
squashing because the evidence-to-implementation chronology is part of the
scientific traceability.