fix(bind): honor OpenAPI date-time format tags

[Copilot]

Adding Swag's format:"date-time" tag to a time.Time field made Echo interpret the OpenAPI name as a Go time layout, rejecting otherwise valid RFC3339 input.

This change recognizes the two OpenAPI format names for time.Time and *time.Time fields in path, query, header, and form binding:

• date-time uses the same standard-library text decoder as an untagged time.Time, accepting RFC3339 timestamps with Z or a numeric offset.
• date-time-local accepts 2006-01-02T15:04:05 with optional fractional seconds and rejects timezone suffixes. Parsing assigns UTC, consistent with Echo's existing custom layouts that omit a timezone. This is an Echo parsing policy; the input itself does not specify UTC.

The formats have distinct semantics in the OpenAPI registry. Other format values continue to be Go layouts. JSON/XML decoding and custom unmarshaler dispatch retain their existing behavior; slice elements retain their existing format-tag behavior.

Validation:

• go test -race --coverprofile=coverage.coverprofile --covermode=atomic ./...
• go vet ./...
• Regression cases cover both formats, scalar and pointer fields, all five affected binding sources, fractional seconds, preserved offsets, invalid dates, missing/forbidden timezones, JSON decoding, and custom types. Existing custom-layout and untagged binding tests also pass.

Fixes #3107