fix(analyzer): allOf entries that redeclare a property lost it on the wire

[giraffesyo]

Closes #120. Found by the corpus test from #119, which vets the generated package rather than only building it.

allOf composes one value, so entries may declare the same property. Each declaration became a field:

type WebhookForkForkee struct {
	AllowForking  *bool  `json:"allow_forking,omitempty"`
	...
	AllowForking2 *bool  `json:"allow_forking,omitempty"`

types.go:24880:2: struct field AllowForking2 repeats json tag "allow_forking" also at types.go:24776
... 247 in that client

The package compiles. encoding/json resolves two fields at one depth carrying one tag by ignoring both, so allow_forking stopped decoding and stopped marshaling while the struct still looked right. A build-only gate cannot see it, which is why #119 added go vet to the corpus test and why this turned up the same day.

GitHub's webhook-fork.forkee is the case: two inline objects, the second refining 78 of the first's 90 properties.

Fix

• One field per property. The first declaration wins the type, which matters little in practice since entries that disagree on type describe a value nothing can satisfy.
• Requirements are read from every entry first. A property required by a later entry is now required by the struct, rather than depending on which entry declared it first, which is what allOf means.
• A property beside an embedded type is untouched. Those live at different depths, Go shadows one with the other, and the tags do not collide.

Worth noting the history: before #96 fixed field-name collisions, this shape failed to compile. That was louder, and in one narrow sense better than a struct that builds and drops data.

Verification

• GitHub: 247 vet failures, now 0, still 1898 types and 242 iterators.
• ACTIVATE, Mealie, Stripe, ledger: build and vet clean, unchanged counts.

Tests

• internal/analyzer/schemas_allof_property_test.go: a property two entries declare is one field, required because one entry requires it, and a property beside an embed is kept.
• testdata/combinations.yaml grows the shape, so the corpus covers it.

gofmt, golangci-lint, go vet ./..., and go test ./... pass.