Improve PIHD sync and PIBD segment handling

[wiesche89]

Description

This PR adds PIHD (Parallel Initial Header Download) header segment sync support and hardens PIBD segment handling during initial sync.
It also incorporates the relevant PIBD fixes from @ardocrat #3823, including improved segment request selection, peer height slack handling, timeout handling, and safer retry behavior.

Main changes:

• Add PIHD header segment sync flow
• Improve PIBD segment selection and validation
• Avoid requesting output/rangeproof/kernel segments before the required bitmap state is available
• Track rejected PIBD segments and handle timed-out peers more defensively
• Improve PIHD/PIBD sync logging for start, abort/fallback, and completion

Compatibility

Legacy header sync and existing fallback behavior remain available for peers that do not support PIHD/PIBD.

Testing

Tested locally on testnet with fresh sync runs.
Tested in testnet farm with grafana.
reachable gateway node grinffindor.org with port 23414, please sync :)

Also verified:

• PIHD starts and completes
• PIBD starts and progresses through segment download and validation
• Invalid/unusable PIBD data is rejected earlier
• Fallback paths remain available

Related Issues

*Fixes #3830
*Partially addresses #3082
*Partially addresses #3289
*Related to #3083
*Related to #3767
*Related to #3292