Preserve protocol blocks and quoted whitespace during BNGL round-trip

[wshlavacek]

Summary

Two coupled fidelity fixes in the BNGL → BNGL round-trip path. The two share the same `parse_actions` refactor, so they're bundled.

1. `begin protocol` / `end protocol` blocks are now preserved

Protocol blocks live INSIDE `begin model` / `end model` and hold a sequence of state-mutating action lines (`setParameter`, `setConcentration`, `simulate`, etc.) that BNG2.pl executes when `parameter_scan({method=>"protocol"})` is invoked.

Previously, `BNGFile.strip_actions` extracted every action-shaped line from the file — including those inside a protocol block — and `BNGParser` routed them into the top-level `ActionBlock`. The regenerated BNGL had no protocol block at all, and BNG2.pl ran the actions at the wrong level.

Fix:

• New `ProtocolBlock(ActionBlock)` in `blocks.py`: same item-list shape as `ActionBlock` but emits its content wrapped in `begin protocol` / `end protocol`.
• `bngmodel` registers `"protocol"` in `_block_order` between `rules` and `actions` so it lands inside the model body, and exposes `add_protocol_block` for the parser's dispatch by name.
• `BNGFile.strip_actions` walks lines tracking an `in_protocol` flag and routes action-shaped lines into `parsed_protocol_actions` instead of `parsed_actions` while inside a protocol block. The `begin protocol` / `end protocol` delimiter lines themselves stay in the stripped output so BNG2.pl re-emits the wrapper.
• `BNGParser.parse_actions` invokes a shared `_parse_action_block` helper twice — once with `ActionBlock` for the top-level actions and once with `ProtocolBlock` for the protocol-block actions. The per-action dispatch logic is factored out into `_parse_action_line`.

2. Quoted whitespace inside action arguments is preserved

Previously `strip_actions` ran `line.replace(" ", "")` on each action line, and `BNGParser.parse_actions` re-ran `re.sub(r"\s", "", action)`. Both were quote-naive, so an action like

```
simulate({method=>"nf",param=>"-v -gml 1000000"})
```

came out as

```
simulate({method=>"nf",param=>"-v-gml1000000"})
```

and NFsim choked on the broken argument string.

The space-collapse is now a quote-aware pass (`_normalize_action_text` + `_strip_comment_outside_quotes` + `_collapse_unquoted_whitespace`) that lives module-level in `bngparser.py`. Tokens inside `"..."` / `'...'` survive intact; unquoted whitespace and trailing `# comments` are still stripped as before.

Test plan

• Existing CI passes
• A model with a `begin protocol`...`end protocol` block round-trips through write_model and re-parses correctly
• `simulate({method=>"nf",param=>"-v -gml 1000000"})` survives round-trip with the quoted spaces intact