fix(spec): keep zero-valued bounds through a gob round-trip

[fredbi]

gob omits any struct field holding the zero value for its type, and flattens a pointer to the value it points at. An optional number that is present and zero travelled as the zero value, was omitted, and came back as a nil pointer: "minimum": 0 on a schema, "maximum": 0 on a parameter and every other bound spelled with a zero were dropped, with no error. Encoding a whole Swagger lost them at any depth, through the encoder this package already advertises.

Schema, Parameter, Header and Items now send which of their optional numbers were present-and-zero as a bitmask alongside the struct, and put the zero back on decode. The encoders sit on those outer types rather than on CommonValidations or SchemaProps because a method on an embedded type is promoted to whatever embeds it: gob would call it for the whole value and drop everything the embedded type does not hold. Swagger and Operation already carry their own encoders for that reason.

TestGob_EveryOptionalNumberIsCarried reads the *float64 and *int64 fields of those four types by reflection, so a bound added later is covered without editing the test, and fails until gob.go carries it.

Round-tripping a mid-sized document through gob costs 153ms and 92MB against 47ms and 26MB before this change, because a GobEncode that returns bytes needs its own encoder per value. JSON round-trips the same document in 39ms and 12MB, so gob is the slower way to copy this model either way.

Change type

Please select: 🆕 New feature or enhancement|🔧 Bug fix'|📃 Documentation update

Short description

Fixes

Full description

Checklist

• I have signed all my commits with my name and email (see DCO. This does not require a PGP-signed commit
• I have rebased and squashed my work, so only one commit remains
• I have added tests to cover my changes.
• I have properly enriched go doc comments in code.
• I have properly documented any breaking change.

[codecov]

Codecov Report

❌ Patch coverage is 96.66667% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 93.19%. Comparing base (69a6c4c) to head (0812163).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
gob.go	96.66%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #310      +/-   ##
==========================================
+ Coverage   93.03%   93.19%   +0.16%     
==========================================
  Files          30       31       +1     
  Lines        2512     2632     +120     
==========================================
+ Hits         2337     2453     +116     
- Misses        175      179       +4     

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