Fix #498, part of #505: EPS image sources read in turn, restore undoes dictionary changes (PLRM)

[bflatastic]

Redoes PR #507's two EPS import fixes using the PostScript Language Reference (3rd ed.) only. It's stacked on #535; review after it, or only the last two commits. Fixes #498. Part of #505.

Fix #498: an image's several data sources are read in turn

• The reference has the image and colorimage operators read multiple data sources in turn, the same amount from each (§4.10 "Images", chapter 8).
• The reader drained each source on its own. When the sources are procedures that read one file a row at a time, the first plane took every component's rows, and the image came out in sheared horizontal bands. That matches [Bug] Rendering glitch / horizontal artifacts when opening EPS vector map files #498.
• Fix: one reader, read_sources, handles single sources, procedure filters and masked images too.
• Tests in tests_images.rs:
  • procedures that read one file, in the dictionary form and the colorimage operand form;
  • separate string sources;
  • rows padded to a whole byte at 1, 2, 4, 12 and 16 bits with an odd width;
  • Flate PNG predictors.
• Mutation check: with the old sequential reading, the procedures test fails.

Part of #505: restore puts dictionaries back as they were at the save (§3.7.3)

• While a save is open, def, store, put, undef and dictionary copy keep the old value of each entry they change in a journal, counted against the memory budget.
• restore undoes those changes, newest first. Restoring a save that is no longer valid raises invalidrestore.
• cachestatus now reports a device's cache sizes instead of zeros.
• Test: a program that counts its open saves in a dictionary under a depth limit reads to its end only when restore puts the count back. It fails without the journal, and also fails with a zero cachestatus.
• Error Text Effect Vector (File Format EPS) #505's reporter sent no file, so this covers what the reference defines, not their specific EPS.

Dropped: #507's rule that stripped a *N suffix from font names. No public spec or user file backs it.

Comments cite PLRM sections. The import fuzz vocabulary covers several sources reading one file, sources of uneven lengths, and save/restore around dictionary changes. ROADMAP updated.

Checks

• Base: EPS tests: interpreter programs written from the PostScript Language Reference #535 (1c449b81), on origin/main @ c0396c0.
• cargo xtask ci: all 7 steps passed (fmt, clippy, test with 3991 tests passing, assets, brands, layers, wasm).

🤖 Generated with Claude Code

[bflatastic]

Full cargo xtask ci passed on the integrated stack; merging.