Refactor: move spending conditions implementation to nut10 module

[TheMhv]

Description

This PR moves the spending conditions implementation to the module that corresponds to the correct NUT specification.

While reviewing the code, I noticed that the SpendingConditions implementation is currently located in nuts/nut11/mod.rs. However, spending conditions are defined in NUT-10, not NUT-11. Keeping this implementation under nut11 can make the module structure slightly confusing for contributors trying to map code to the corresponding NUT specifications.

This change relocates the relevant implementation to the nut10 module so the code structure better reflects the specification layout.

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Notes to the reviewers

• Create a folder nut10/ for module of NUT-10
• Move SpendingConditions and Conditions from nut11/mod.rs to nut10/spending_conditions.rs
• Move all NUT-10 related errors to nut10/error.rs
• Move Secret implementation to nut10/secret.rs
• Move SpendingConditions::new_p2pk, extract_signatures_from_witness and verify_sig_all_p2pk functions to nut11/mod.rs
• Move SpendingConditions::new_htlc, SpendingConditions::new_htlc_hash, verify_htlc_preimage and verify_sig_all_htlc to nut14/mod.rs
• Move Tag and TagKind to nut10/tag.rs

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Suggested CHANGELOG Updates

CHANGED

• NUT-10 Spending Conditions

ADDED

REMOVED

FIXED

• Spending Conditions implementation is placed in nut11 instead of NUT-10 module #1705

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Checklist

• I followed the code style guidelines
• I ran just final-check before committing

[TheMhv]

I could further separate and modularize the Spending Conditions code, but that's not the purpose of this PR. What do you think about discussing this?

[thesimplekid]

This moves some this to a better place but leaves other fns not in the files of their nut.

[thesimplekid]

Looks good. I think we should reduce the visibility of some of the helper fns we have so they are not in the public api. What do you think @crodas

[thesimplekid]

closes: #395