eds: Add first-class support for CiA 306 ObjFlags and Denotation

[bizfsc]

ObjFlags (UNSIGNED32 bitfield) and Denotation (DCF-only string) are standard CiA 306 fields that were previously silently dropped. This PR adds first-class support for both.

Changes

• ODVariable, ODRecord and ODArray gain an obj_flags: int = 0 attribute.
• ODVariable gains a denotation: str = "" attribute.
• New _get_obj_flags(eds, section) helper reads and validates the ObjFlags integer value.
• ObjFlags is parsed for VAR/DOMAIN (via build_variable()), ARRAY and RECORD top-level objects.
• ObjFlags is exported whenever non-zero.
• Denotation is read in build_variable() and written only in DCF mode (device_commisioning=True), matching the CiA 306 specification.

Tests

• test_reading_obj_flags — VAR with ObjFlags=0x1 reads back correctly
• test_reading_obj_flags_default — standard objects default to 0
• test_roundtrip_obj_flags — full EDS export/import cycle preserves obj_flags
• test_denotation_roundtrip_dcf — denotation survives a DCF round-trip
• test_denotation_not_exported_in_eds_mode — denotation is absent in plain EDS export

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[bizfsc]

Is this YAGNI?

[acolomb]

Frankly, I never heard of it. But now that I have, I had an immediate idea where it could be used in my code, replacing a previous workaround.

Some controllers have extra objects for "user variables" which can be utilized in a user-supplied small PLC program on the device. The function of this custom program defines what the variable is really used for (denotation), yet the device manufacturer can only assign a generic name of "user variable 1" in the generic device EDS. That sounds like a perfect application of this less widespread option.

The ObjFlags option also seems to solve a problem I've previously worked around by hard-coding objects to skip.

I'll have to take a deeper look to really judge if it works like I imagine. And get better acquainted with their definition in CiA 306.