go/signature: apply options on registered contexts

[pro-wh]

when allowing unregistered signature contexts, still apply options for contexts that are registered

[codecov]

Codecov Report

Merging #4591 (504af66) into master (ec74d2c) will increase coverage by 0.04%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4591      +/-   ##
==========================================
+ Coverage   66.44%   66.49%   +0.04%     
==========================================
  Files         428      428              
  Lines       48512    48512              
==========================================
+ Hits        32235    32256      +21     
+ Misses      12336    12318      -18     
+ Partials     3941     3938       -3     

Impacted Files	Coverage Δ
go/common/crypto/signature/signer.go	96.49% <100.00%> (+1.75%)	⬆️
...onsensus/tendermint/apps/beacon/state/state_vrf.go	73.33% <0.00%> (-13.34%)	⬇️
go/worker/beacon/tx_retry.go	90.47% <0.00%> (-4.77%)	⬇️
go/storage/mkvs/insert.go	87.75% <0.00%> (-4.09%)	⬇️
go/worker/common/p2p/rpc/client.go	79.77% <0.00%> (-3.38%)	⬇️
...consensus/tendermint/apps/registry/transactions.go	54.83% <0.00%> (-2.95%)	⬇️
go/oasis-node/cmd/ias/auth_registry.go	65.81% <0.00%> (-2.57%)	⬇️
go/storage/mkvs/lookup.go	75.00% <0.00%> (-2.09%)	⬇️
go/worker/beacon/worker_vrf.go	64.34% <0.00%> (-1.74%)	⬇️
go/worker/common/p2p/rpc/peermgmt.go	76.43% <0.00%> (-1.28%)	⬇️
... and 14 more

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[kostko]

Let's also backport this.

[pro-wh]

gonna add a test to cover that unregistered malformed context branch while I'm here

[pro-wh]

backports opened 👍