refactor(dpp): align pre_programmed_distribution token update validation with reachable update surface

[PastaPastaPasta]

Summary

pre_programmed_distribution exists on TokenDistributionRulesV0, but the token configuration update validation helper does not mention it. This is currently a code consistency issue, not a reachable security vulnerability.

Current behavior

• pre_programmed_distribution is present on TokenDistributionRulesV0.
• validate_token_config_update_v0 validates other token distribution fields but does not explicitly handle pre_programmed_distribution.
• Full data contract updates already reject token configuration changes wholesale.
• The dedicated token config update transition does not expose any TokenConfigurationChangeItem variant that can mutate pre_programmed_distribution.

Because there is no reachable mutation path today, this should not be treated as an open security issue.

Why track this

This is still a maintenance footgun:

• The validation helper and the token distribution struct are out of sync.
• A future change could add a reachable update path for pre_programmed_distribution and accidentally rely on the existing helper, assuming the field is already covered.
• That could turn the current inconsistency into a real authorization or immutability bug.

Suggested resolution

Pick one of these and document the intended behavior clearly:

1. Make pre_programmed_distribution explicitly immutable in validate_token_config_update_v0.
2. Introduce full change-control support for pre_programmed_distribution if post-creation updates are intended.
3. Add comments or assertions that clarify the field is intentionally excluded because it is not part of the reachable token config update surface.

Acceptance criteria

• The intended mutability of pre_programmed_distribution is explicit in code.
• The validation/update helpers and the reachable token config update surface are aligned.
• Tests cover the intended behavior so future feature work cannot silently make this field mutable without corresponding validation.

Relevant files

• packages/rs-dpp/src/data_contract/associated_token/token_distribution_rules/v0/mod.rs
• packages/rs-dpp/src/data_contract/associated_token/token_configuration/methods/validate_token_configuration_update/v0/mod.rs
• packages/rs-dpp/src/data_contract/associated_token/token_configuration_item.rs
• packages/rs-dpp/src/data_contract/associated_token/token_configuration/methods/apply_token_configuration_item/v0/mod.rs
• packages/rs-dpp/src/data_contract/methods/validate_update/v0/mod.rs

Investigation note

Security review conclusion: the previously reported issue was refuted as non-exploitable in current and historical reachable paths, because pre_programmed_distribution has not been exposed through the token config update change-item surface, and whole-contract token config mutations are rejected.