feat(libRequest): add optional JSON body binding modes

[hmmftg]

Problem

libRequest.parseRequest treats every body parse failure as fatal (ERROR_IN_GET_REQUEST_BODY → 400). For endpoints where the body is optional — e.g. POST /api/card/:cardNumber/harim, which takes all required input from the path and only reads cvv2/expiry when present — a POST with Content-Length: 0 is rejected even though the contract allows it. Clients that send no body (e.g. Swagger UI when no requestBody is defined) get an unexpected 400.

Design

• New sentinel webFramework.ErrEmptyBody, returned by RequestParser.GetBody implementations when the body is absent or zero-length (wrappable; callers use errors.Is). Empty body is now distinguishable from a successful bind.
• Two new libRequest.Type values, appended at the end of the const block so existing iota values — which are JSON-serialized and persisted — are unchanged:
  • JSONOptional — binds JSON when present; empty body yields the zero-valued request.
  • JSONWithURIOptional — same optional body semantics; URI binding stays mandatory.
• requestTypeEnum.go regenerated via enumer (v1.7.2).
• Parsers: libGin maps io.EOF → sentinel; libFiber returns it when len(Body()) == 0; libNetHttp returns it for absent/empty bodies (previously returned nil); FakeParser gains a BodyError field and honors the sentinel; TestingParser honors it for nil/empty fixtures.
• TestingParser.setTarget no longer panics: it previously called Set on an unaddressable reflect.Value; now uses Elem() with kind/assignability guards.

Backwards compatibility

• JSON and JSONWithURI still fail on empty bodies with ERROR_IN_GET_REQUEST_BODY — only the new modes tolerate the sentinel.
• One intentional alignment: libNetHttp previously accepted empty bodies under required JSON; it now matches Gin/Fiber and rejects them.
• Struct validation (libValidate.ValidateStruct) still runs for optional modes on the zero-valued request — optional body fields need omitempty/non-required tags.
• Malformed bodies still return 400 in all modes.

Usage

handlers.HandlerParameters[Req, Resp]{
    Body: libRequest.JSONWithURIOptional, // body optional; URI params still bound
}

Testing

• Table-driven tests: optional modes with empty body (success), valid body (bound + validated), malformed body (400), missing required URI param (400), plus regression coverage that JSON/JSONWithURI still reject empty bodies.
• Per-parser ErrEmptyBody assertions for Gin, Fiber, and net/http.
• go build ./..., go test ./..., go vet ./... all green.