feat: parse floating-point text through the standard library

README.md

@@ -75,6 +75,8 @@ numeric typing follows contextual rules within Honey's current `int` and `float`
 
 the conversion policy is value-preserving by default: any future implicit widening must preserve every value of the source type, not merely the value observed at one use. narrowing, potentially inexact integer-to-float conversion, float-to-integer conversion, and signedness changes that cannot preserve the full source range require an explicit operation. integer arithmetic remains checked rather than wrapping; floating arithmetic retains IEEE rounding.
 
+`@std/strconv.parse_float(allocator, text)` parses a complete borrowed `[]u8` decimal into `f64`. it accepts an optional sign, decimal point, and exponent; whitespace, embedded NUL bytes, trailing input, hexadecimal, infinities, and NaNs return `invalid_number`. finite subnormals and signed zero are preserved; overflow and nonzero values rounded to zero return `out_of_range`. allocation failures propagate as `out_of_memory`, and temporary storage is always released. the Darwin backend uses libc's C-locale conversion without changing the process locale; rounding follows the caller's floating-point rounding mode. numeric lowering uses this interface, keeping exact integer-to-float validation compiler-specific.
+
 type errors carry source spans and diagnostic identities; invalid operands propagate their existing identity without duplicate errors, while independent expressions, arguments and nested bodies are still checked. inference cycles without a type anchor are diagnosed. function signatures are checked independently of their bodies. bare `return` and same-line `return expression` are supported inside function bodies and must match the declared result type. nonvoid return-path checking is structural: every path must return or terminate in a diagnostic trap, and both conditional successors are considered without constant folding. a missing `else` or a loop permits fallthrough, even for a literal `true` condition; a later return can close that path. statements after a return and untaken branches or loops are still type-checked but are not executed.
 
 `lower.lower` turns the checked AST and binding table into an owned `@source/ir` module. functions, globals, local slots and instruction-result temporaries have explicit IDs; typed instructions execute in source evaluation order and basic blocks end in jump, conditional-branch, return or diagnostic-trap terminators. conditional arms join only when execution can continue; loops use condition/body/exit blocks and backedges. short-circuit expressions use branches and synthetic boolean local slots to merge results; call arguments are packed in the block reached after evaluating them. local slots and temporaries are function-wide, without SSA or phi nodes. literals are parsed and strings decoded during lowering; the module retains no AST, binding-table or source-buffer references. release it with `ir.deinit`; keep and reuse the diagnostic store used during lowering so diagnostic IDs remain valid. the IR is target-independent and is intended to feed later native backends as well as the current interpreter.