[WIP] regtest: align activations with Bitcoin Core

[starius]

Change Description

Set regtest buried heights to match Core: BIP34/65/66 at height 1 and make CSV/SegWit/Taproot always active. Added regtest coverage for header version floors, coinbase height enforcement, and deployment state to ensure we now reject the blocks Core rejects and accept the ones Core accepts.

Updated package fullblocktests to generate BIP34-compliant blocks.

Test helpers now set prev block height to 0 (not the default -1) so generated blocks start at height 1 and satisfy coinbase height rules.

Depends on #2467 to pass test TestFullBlocks. Currently it is failing with:

fullblocks_test.go:274: block "b61dup" (hash 42cad0fe0aed82595a3e38d798d5d0099aa7f77c74cda4d3f3a0c4ce1440496a, height 119) does not have expected reject code -- got ErrMissingTxOut, want ErrOverwriteTx

Steps to Test

make unit

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