*: specify RFC6979 signer as mandatory where appropriate

Refs. #209.

Signed-off-by: Roman Khimov <roman@nspcc.ru>

client/client.go

@@ -159,7 +159,10 @@ type PrmInit struct {
 // SetDefaultSigner sets Client private signer to be used for the protocol
 // communication by default.
 //
-// Required for operations without custom signer parametrization (see corresponding Prm* docs).
+// Optional if you intend to sign every request separately (see Prm* docs), but
+// required if you'd like to use this signer for all operations implicitly.
+// If specified, MUST be of [neofscrypto.ECDSA_DETERMINISTIC_SHA256] scheme,
+// for example, [neofsecdsa.SignerRFC6979] can be used.
 func (x *PrmInit) SetDefaultSigner(signer neofscrypto.Signer) {
 	x.signer = signer
 }

container/container.go

@@ -476,7 +476,9 @@ func ReadDomain(cnr Container) (res Domain) {
 // and writes it into dst. Signature instance MUST NOT be nil. CalculateSignature
 // is expected to be called after all the Container data is filled and before
 // saving the Container in the NeoFS network. Note that мany subsequent change
-// will most likely break the signature.
+// will most likely break the signature. signer MUST be of
+// [neofscrypto.ECDSA_DETERMINISTIC_SHA256] scheme, for example, [neofsecdsa.SignerRFC6979]
+// can be used.
 //
 // See also VerifySignature.
 func CalculateSignature(dst *neofscrypto.Signature, cnr Container, signer neofscrypto.Signer) error {

pool/pool.go

@@ -998,6 +998,8 @@ type InitParameters struct {
 }
 
 // SetSigner specifies default signer to be used for the protocol communication by default.
+// MUST be of [neofscrypto.ECDSA_DETERMINISTIC_SHA256] scheme, for example,
+// [neofsecdsa.SignerRFC6979] can be used.
 func (x *InitParameters) SetSigner(signer neofscrypto.Signer) {
 	x.signer = signer
 }