feat: add typed API for flamegraph and collapse

[jonhoo]

Inferno's library API was purely text-based: collapsers produce "stack;frames count\n" lines, and flamegraph parses them back. Downstream tools with structured stack data had to round-trip through text, causing escaping issues, wasted work, and loss of type safety (issues #30, #164, #270).

This commit adds a typed API alongside the existing text path. The core type is Sample<S>, generic over the stack iterator, which replaces the text line "main;foo;bar 42". Three new entry points accept iterators of Sample: from_sorted_stacks (requires pre-sorted input), from_stacks (sorts internally), and flame_chart_from_stacks (preserves time ordering). On the collapse side,
Collapse::collapse_to_stacks returns a FoldedStacks wrapper whose samples() method yields typed Sample values for direct rendering without text serialization. CollapsePrivate implementors get an efficient override that skips text entirely; other Collapse implementors get a default that round-trips through text that they can override if able.

Options is now Clone and has no lifetime parameter. The mutable palette_map reference moves to a separate parameter on all public functions, and text-processing fields (no_sort, reverse_stack_order, flame_chart, base) move to a new PreProcessingOptions struct that is only needed by the text-based entry points.

This is a breaking API change, hence the version bump to 1.0.0-rc.1.

[codecov]

Codecov Report

❌ Patch coverage is 70.60932% with 82 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.84%. Comparing base (51423f4) to head (7dd0e67).

Files with missing lines	Patch %	Lines
src/collapse/mod.rs	0.00%	62 Missing ⚠️
src/collapse/common.rs	30.76%	18 Missing ⚠️
src/flamegraph/merge.rs	96.66%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #358      +/-   ##
==========================================
- Coverage   91.22%   89.84%   -1.38%     
==========================================
  Files          21       21              
  Lines        4272     4481     +209     
==========================================
+ Hits         3897     4026     +129     
- Misses        375      455      +80     

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[jonhoo]

This took me forever to get around to, but here's finally a first draft of a more reasonable crate API for inferno.

Would love to get input from the various people interested in #30, #164, and #270, like @koute, @Licenser, @Kixiron, @itamarst, and @stepancheg.

I also figure that once we land this, we're probably ready to mark inferno as 1.0 👀